Chapter 11: Introduction to Genetics

Genetics – the branch of biology that studies heredity

Heredity – the passing on of traits from parent to offspring

Chromosome – the genetic material (DNA) that is passed from generation to generation

Genes – segment of DNA that codes for a trait

Alleles – different forms of genes

2 Types of Alleles

Dominant

Observed trait, or the trait that is expressed

Capital letter (T)

Recessive

Trait that is masked or hidden

Lower case letter (t)

You inherit 2 alleles for each gene. One from mom and one from dad.

Homozygous – two same alleles for a trait

Homozygous Dominant – 2 dominant alleles (TT)

Homozygous Recessive – 2 recessive alleles (tt)

Heterozygous – 2 different alleles for a train (Tt)

Two organisms can look alike but have different gene combinations

Phenotype – the trait you see

Genotype – the actual gene combination

You can’t always know an organisms genotype simply by looking at its phenotype

Genes are lined up on chromosomes

A chromosome can contain a thousand or more genes

11-1 The Work of Gregor Mendel

Gregor Mendel

Carried out the first important studies of heredity

Father of genetics

He was a monk in an Austria Monastery that was a great scientific research center

First person to predict how traits are transferred from generation to generation

He studied pea plant traits

Pea plants reproduce sexually and contain both male and female gametes

Self Pollination – male and female gametes from the same plant unite

Pure-Bred – the offspring of 1 parent and has identical genes (clone)

Cross Pollination – male and female gametes from different plants unite

Hybrid – the offspring of 2 parents that have different forms of a trait

Mendel carefully controlled his experiments and only studied one pea trait at a time

One trait he studied was height of a pea plant

Mendels Monohybrid Crosses

Monohybrid Cross – a genetic cross involving one trait

Tall Pea PlantShort Pea Plant

Self Pollinate

Tall Pea PlantShort Pea Plant

Cross Pollinate

4 Tall Pea Plants

Self Pollinate

3 Tall and 1 Short

From this monohybrid cross Mendel concluded…

Pea plant had two alleles of the gene that determined its height

The allele for Tall is dominant – T

The allele for Short is recessive – t

If the plant was tall its genotype was TT or Tt

If the plant was short its genotype was tt

The Law of Segregation

To explain why in the F1 generation the trait for shortness disappeared and then reappeared in the F2 generation Mendel formulated his Law of Segregation

He concluded that the F1 plants had a allele for tallness and an allele for shortness

Because they have two different alleles they can produce 2 different types of gametes (tall and short)

During fertilization these gametes randomly pair to produce 4 possible combinations of alleles

Law of Segregation – the members of each pair of alleles separate when gametes are formed

Punnett Square - used to predict and compare the genetic variations that will result from a cross

Examples of Monohybrid Punnett Squares

Ex. Mom genotype: __Tt____

Dad genotype: __Tt____

T / t
T / TT / Tt
t / Tt / tt

Mendel’s Dihybrid Crosses

Mendel did another cross which he used pea plants that differed from each other in two traits rather than one

Dihybrid Cross – a cross involves two traits

Will the two traits stay together in the next generation or will they be inherited independently of each other?

Round Yellow Pea SeedWrinkled Green Pea Seed

Self Pollinate

Round Yellow Pea SeedWrinkled Green Pea Seed

Cross Pollinate

4 Round Yellow Pea Seeds

Self Pollinate

9 Round Yellow 3 Round Green 3 Wrinkled Yellow 1 Wrinkled Green

The Law of Independent Assortment

Law of Independent Assortment – genes for different traits can segregate independently during the formation of gametes

The gametes, R (round), r (wrinkled), Y (yellow), and y (green), will separate from each other and recombine in 4 different ways RY, Ry, rY, and ry

If the alleles were inherited together, only two kinds of pea seeds would have been produced RY (round yellow) and ry (wrinkled green)

This Law does not hold true all of the time. If the genes are on different chromosomes it is true, but if they are on the same chromosome it is not true.

Examples of Dihybrid Punnett Squares

Beyond Dominant and Recessive Alleles

Not all genes show simple patterns of dominant and recessive alleles

In most organisms genetics is more complicated, because the majority of genes have more than two alleles.

Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes

Incomplete Dominance

Incomplete Dominance – the phenotype of the heterozygote is intermediate between the dominant and recessive

Ex. Red Snapdragon RR X White Snapdragon WW

Pink Snapdragon RW

Neither allele is completely dominant over the other

Codominance

Codominant Alleles – the phenotypes of both homozygotes are produced

Both allele are expressed equally

Ex. White Horse WW X Tan Horse TT

Roan Horse WT

Multiple Alleles

It is common for more than two alleles to control a trait in a population

Multiple Alleles – traits controlled by more than two alleles

Ex. ABO Blood Groups

Human blood types are determined by the presence or absence of certain molecules on the surface of red blood cells

The best known are ABO groups and Rh groups

ABO Groups

3 Alleles for blood types IA (A), IB (B), i (O)

IA (A), IB (B) are dominant

i (O) with is recessive

4 Blood Types

Blood Type / Possible allele combinations
A / IAIA or IAi (AA or AO)
B / IBIB or IBi (BB or BO)
AB / IAIB (AB)
O / ii (OO)
Blood Type / Can Give Blood To / Can Get Blood From
A / A or AB / A or O
B / B or AB / B or O
AB / AB / A, B, AB, and O
O / A, B, AB, and O / O

Rh Groups

Stands for rhesus monkey

+ allele is dominant

- allele is recessive

Universal Donor – O blood and is most common

Universal Recipient – AB blood and is rare

If blood types are not matched during a blood transfusion, the red blood cells will clump together causing death

Blood typing is also useful in determining parentage

Examples of Blood Types with Punnett Squares

Chapter 11: Introduction to Genetics

Genetics –

Heredity –

Chromosome –

Genes –

Alleles –

2 Types of Alleles

Dominant

Recessive

You inherit _____ alleles for each gene. One from ______and one from ______.

Homozygous –

Homozygous Dominant –

Homozygous Recessive –

Heterozygous –

Two organisms can look alike but have different gene combinations

Phenotype –

Genotype –

You can’t always know an organisms ______simply by looking at its ______

Genes are lined up on ______

A chromosome can contain a thousand or more genes

11-1 The Work of Gregor Mendel

Gregor Mendel

Carried out the first important studies of ______

He was a ______in an Austria Monastery that was a great scientific research center

First person to predict how traits are transferred from generation to generation

He studied ______traits

Pea plants reproduce ______and contain both male and female gametes

Self Pollination –

Pure-Bred –

Cross Pollination –

Hybrid –

Mendel carefully controlled his experiments and only studied ______pea trait at a time

One trait he studied was height of a pea plant

Mendels Monohybrid Crosses

Monohybrid Cross –

Tall Pea PlantShort Pea Plant

Self Pollinate

Cross Pollinate

Self Pollinate

From this monohybrid cross Mendel concluded…

Pea plant had two alleles of the gene that determined its height

The allele for Tall is ______– _____

The allele for Short is ______– _____

If the plant was tall its genotype was ______or ______

If the plant was short its genotype was ______

The Law of Segregation

To explain why in the F1 generation the trait for shortness disappeared and then reappeared in the F2 generation Mendel formulated his Law of Segregation

He concluded that the F1 plants had a allele for ______and an allele for ______

Because they have two different alleles they can produce 2 different types of gametes (tall and short)

During fertilization these gametes ______pair to produce _____ possible combinations of alleles

Law of Segregation –

Punnett Square -

Examples of Monohybrid Punnett Squares

Ex. Mom genotype: ______

Dad genotype: ______

Mendel’s Dihybrid Crosses

Mendel did another cross which he used pea plants that differed from each other in two traits rather than one

Dihybrid Cross –

Will the two traits stay together in the next generation or will they be inherited independently of each other?

Round Yellow Pea SeedWrinkled Green Pea Seed

The Law of Independent Assortment

Law of Independent Assortment –

The gametes, R (round), r (wrinkled), Y (yellow), and y (green), will separate from each other and recombine in 4 different ways _____, _____, _____, and _____

If the alleles were inherited together, only two kinds of pea seeds would have been produced _____ (round yellow) and _____(wrinkled green)

This Law does not hold true all of the time. If the genes are on different chromosomes it is true, but if they are on the same chromosome it is not true.

Examples of Dihybrid Punnett Squares

Beyond Dominant and Recessive Alleles

Not all genes show simple patterns of dominant and recessive alleles

In most organisms genetics is more complicated, because the majority of genes have more than two alleles.

Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes

Incomplete Dominance

Incomplete Dominance –

Ex. Red Snapdragon _____ X White Snapdragon _____

Pink Snapdragon _____

Neither allele is completely dominant over the other

Codominance

Codominant Alleles –

Both allele are expressed equally

Ex. White Horse _____ X Tan Horse _____

Roan Horse _____

Multiple Alleles

It is common for more than two alleles to control a trait in a population

Multiple Alleles –

Ex.

Human blood types are determined by the presence or absence of certain molecules on the surface of red blood cells

The best known are ______groups and ______groups

ABO Groups

3 Alleles for blood types ______, ______, ______

______, ______are dominant

______with is recessive

4 Blood Types

Blood Type / Possible allele combinations
Blood Type / Can Give Blood To / Can Get Blood From

Rh Groups

Stands for “______”

_____ allele is dominant

_____ allele is recessive

Universal Donor –

Universal Recipient –

If blood types are not matched during a blood transfusion, the red blood cells will clump together causing death

Examples of Blood Types with Punnett Squares

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