Chapter 12 - Inheritance Patterns and Human Genetics

I. Chromosomes and Inheritance

A. Terms

1. Autosome- any chromosome but the sex chromosomes

[humans have 44 (22 pairs)]

2. Sex Chromosomes- determine the sex of the organism

  • in humans X and Y determine the sex in the offspring
  • XX= female
  • XY= male

B. Sex Determination (Morgan)

1. Drosophila (fruit fly)

a. 4 pairs homologous chromosomes (1 X/Y pair and 3

autosomal pairs)

b. one pair different in males

1) chromosome same in both sexes called X

shorter, hooked shaped one in male called Y

2) hypothesized them to be sex chromosomes (determine sex)

c. males XY and females XX

1) male gametes contain X or Y , female only X

2. Sex Linkage (Morgan) (showed that specific gene was on a chromosome)

a. hypothesized more genes on X since it is larger

b. fruit flies usually have red eyes

(found a male with white eyes)

c. white eyed males X red eyed female(homozygous)

F1 all red eyed

red eyed male X red eyed female (now will be

heterozygous)

F2 3 red eyed : 1 white eyed (all white eyed were males)

d. hypothesized the gene was on the X chromosome

e. sex linkage - presence of a gene on a sex chromosome (trait is linked to sex)

1) X linkage and Y linkage (holandrichandout)

C. Linkage Groups

1. Morgan sometimes found traits separating independently and other traits did not

2. linkage group - all the genes located on one chromosome

a. 2 or more genes on same chromosome said to be linked

b. experiments show genes are linked on all chromosomes

P1GGLL X ggll

F1GgLl (all gray body, long wing)

GgLl X GgLl

Morgan hypothesized the following:

F2 not linked should be 9:3:3:1

linked should be 3:1

results of cross approximately 3:1 (therefore should be linked), but cross unexpectedly produced several gray short winged (Ggll) and several black long winged (ggLl)

3. crossing over

a. Morgan test crossed an F1 with homozygous recessive

GgLl X ggll

some offspring gray, short and some black, long

b. not possible if G and L always inherited together

c. hypothesized alleles on 2 homologous chromosomes exchanged places (crossing over)

1)occurs in synapsis (prophase I)

2) increases variety in offspring

If either had not been linked…

D. Chromosome Mapping

1. crossing-over showed genes were at fixed positions

on chromosomes

2. genes in a line like a string of beads

3. the farther apart 2 genes are the greater the

frequency of crossing-over

4. results of crossing-over appear in offspring

as new combinations of traits

a. the greater the % of offspring that show

the new comb., the farther apart the genes are

5. breeding experiments can determine how

frequently genes for particular traits are separated

in the offspring

6. chromosome map - shows linear sequence

of genes on chromosome

II. Human Genetics

A. Genetic Traits and Disorders

1. Single allele traits (more than 250)

a. can be due to autosomal recessive or dominant alleles (Table 12-1p. 228)

1) cleft chin, freckles, free earlobes, webbed fingers (dominant)

2) PKU, sickle cell anemia (recessive)

PKU can’t make enzyme to break down amino acid, phenylalanine - it accumulates, destroys brain cells - severe mental retardation

b. genetic marker - short section of DNA that is known to have close association with particular gene nearby

2. Multiple allele traits

a. controlled by 3 or more alleles of same gene

b. blood type alleles - IA, IB, i

1) IAand IB are codominant (both expressed when together) and both are dominant to i

2) phenotypegenotype

type AIAIA : IAi

type BIBIB: IBi

type ABIAIB

type Oii

3) example I A IB X IBi

genotypic ratio

phenotypic ratio

3. Polygenic traits (controlled by 2 or more genes)

a. each gene has a small additive effect

b. continuous variation shown in the trait

1) skin color, eye color, foot size, height, weight, intelligence

4. Complex Characteristics

a. characters that are influenced strongly by environment and by genes

b. most complex traits are also polygenetic traits

c. skin color- expose to the sun causes the skin to become darker, no matter what the genotype is

d. Height- influenced by an unknown # of genes, but also a person’s nutrition and diseases

e. breast cancer, diabetes, heart disease, stroke, and schizophrenia

5. X-linked traits

a. color-blindness, hemophilia, Duchenne muscular dystrophy

b. many other genes code for proteins needed for normal functions

6. Sex-influenced traits(baldness, beard and breast development)

a. presence of male or female sex hormones influences expression of certain traits

b. pattern baldness

Pattern baldness
Phenotypes / Male / Female
Bald / BB and Bb / BB
Normal hair / bb / bb and Bb

*Presence of male hormone causes single B to be expressed (if there are two “b’s” then imagine that only one will change to “B.”

c. genes on autosomes so both sexes can have same genotype, but the trait only expressed in one sex

7. Nondisjunction disorders (Fig. 12-3p. 230) referring to

humans

a. monosomy - 45 chromosomes in zygote (one copy of a particular chromosome)

b. trisomy - 47 chromosomes in zygote (three copies of a particular chromosome)

c. Down syndrome - 47 chromosomes (trisomy #21)both sexes

d. Turner syndrome - 45 chromosomes (XO) - females

e. Klinefelter syndrome - 47 chromosomes (XXY) - males

f. Super female - 47 chromosomes (trisomy of X) (XXX)

g. XYY (males)

ReviewQuestions

C. Detecting Genetic Disorders

1. genetic screening (for those with history of genetic disorders) - karyotype, examine blood for presence or absence of certain proteins

2. genetic counseling - medical guidance informing individuals

of potential problems for offspring

3. amniocentesis - some amniotic

fluid removed at 14-16 weeks

(analyze fetal cells and proteins,

make karyotype)

4. chorionic villi sampling - sample of tissue between uterus and placenta at 8-10 weeks (villi same genetic makeup as embryo) - make karyotype

5. genetic screening after birth for PKU

6. ultrasound– sonogram (use sound waves)

7. fetoscopy - view fetus, take picture

III. Blood Transfusions and Rh Factor

Antibody: a protein produced to bind to an antigen,protects body from foreign substances (in plasma)

Antigen: a protein that stimulates a response from the immune system (on the RBC’s)

A. Transfusions

1. concerned with antibodies of recipient

a. antibodies agglutinate (clump) antigens

TypeAntigensAntibodies Can receiveCan donate

fromto

A A bA,OA, AB

B BaB,OB,AB

AB A & B noneA,B,AB,OAB

O none a & bO A,B,AB,O

Picture

B. Rh Factor

1. another antigen on RBC’s

85% Rh + (have antigen)

15% Rh - (no antigen)

2. Rh + blood given to Rh - person

a. Rh - person develops antibodies against Rh antigen

b. little problem on 1st transfusion but subsequent one could be fatal

C. Erythroblastosis fetalis

(RBC) (destruction) (fetus)

1. mother Rh -, father Rh +, baby Rh +

2. 1st child (Rh +)

a. if any leakage across placenta to uterine blood vessels, mother will make antibodies against Rh antigen

b. antibodies not made fast enough to affect baby

3. subsequent child (Rh +)

a. antibodies already present will destroy baby’s RBC’s

b. can transfuse baby with Rh - blood in utero (dangerous)

4. Rhogam shot

a. given to mother both before delivery and within 72 hours

of birth of child

b. destroys any Rh + blood antigens mother may have gotten from child (contains anti Rh antibodies) in order

to prevent mother from making antibodies (making

antibodies could cause anemia, kidney failure, shock in

mother) which would attack baby’s blood cells