COMPLEX INHERITANCE and COMMON GENETIC DISORDERS

Chapter 11 Fill-in-blank Notes

Use your text to read and learn about each topic, filling in the blanks below.

Recessive Disorders (p. 296-298): most human disorders are recessive, so individuals must have two recessive alleles to show the disorder. Examples:

Cystic fibrosis –

Albinism

Tay-Sach’s disease –

Galactosemia

PKU (phenylketonuria) - inability to breakdown phenylalanine in blood;

tested with foot prick test shortly after birth. Can cause mental

impairment and lack of normal skin pigmentation. Babies and children

with it must maintain a strict diet low in this amino acid.

Discuss some dangers of inbreeding –

Dominant disorders(p. 298): some human disorders due to dominant alleles,

some non-lethal. Just because a gene is dominant does NOT mean that

there is more of it in a population. In fact, lethal dominant genes are

much less common than lethal recessive genes because it affects anyone

who gets it, so offspring may not survive long enough to reproduce. In

this way it reduces the number of lethal genes in the population.

Examples:

Huntington’s disease –

Achondroplasia –

Polydactyly – extra fingers or toes – usually underdeveloped appendages

Pedigrees (p. 299-301)– family trees used to trace the inheritance of particular traits over generations

Carriers – people who carry one copy of the recessive allele for a disorder

but do not exhibit symptoms

What do the symbols seen in a pedigree illustrate? Draw and describe the codes as listed on p. 299.

How are pedigrees used to infer genotypes?

How are pedigrees used to predict disorders?

What are some limitations of using pedigrees to predict disordersl?

Codominant Disorders (p 302-303) See previous notes provided. Contrast Incomplete dominance and codominance below.

Sickle cell disease

-

Malaria Connection (describe how it is associated with sickle cell anemia)

Multiple Alleles (p. 304-305)

See previous notes, and list some examples of characteristics determined by multiple alleles from text and notes below.

Epistasis(p. 305)

Describe and give example.

Sex Chromosomes(p. 305-306)

Separate sexes: X-Y system in humans and most animals

What are some systems to determine sex which exist in other organisms?

by chromosome number (not by sex chromosomes) – Ex: bees and ants

Monoecious – having individuals who produce both sperm and eggs (usually refers to plants) Ex: corn plants

Hermaphroditic–condition in which an organism has both male and female reproductive organs and functions as both a male and a female in sexual reproduction by producing both sperm and eggs.Ex: earthworms, garden snails

P 306 What does it mean for an X chromosome to be inactivated? How does this occur, and what may it impact?

Sex-Linked Traits (p. 307-308) See previous class notes and problems.

Describe the 2 sex-linked traits discussed in your text.

Polygenic Traits(p. 309)

Explain why your book shows the skin color example under a bell curve.

EnvironmentalInfluences (p. 309 -310)

Describe how the environment may influence expression of certain traits.

Twin studies – How do twin studies help us determine environmental influences?

Fetal testing p. 314-315 to detect genetic disorders – Describe pros and cons of each:

Amniocentesis –

Chorionic villus sampling (CVS) –

Fetal Blood Sampling -

Ultrasound –ultrasonic Sound waves bounced off baby to form an image

of the fetus, Neither baby nor mother can hear the sound, noninvasive with

no known risk

Fetoscopy – a needle-thin tube with a viewing scope is inserted into

uterus, giving a direct view of the fetus. Up to 10% risk – higher than any

of the others above

Other important terms-

Genetic screening – testing of prospective parents for alleles associated

with a particular genetic disorder in order to assess, discuss, and weigh any

risks prior to pregnancy; is combined with education and genetic counseling

Linked genes – genes located close together on same chromosome so

they are usually inherited together

Crossing over produces new allele combinations and results in some

unexpected results and percentages from crosses of known genotypes

Recombination frequency – percentage of recombinants shows the

occurrence of crossing over

Mapping genes – recombination data helps scientists determine gene

locations on a chromosome and their distances from one another; mapping

is done with advanced DNA technology today

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