Genetics Test 3

Gamete formation

Meiosis

What are the two parts of sexual reproduction?

• Meiosis

• Fertilization

Small gametes

Male

Large gametes

Female

What process causes the genetic variation seen in offspring produced by sexual reproduction?

Meiosis

both sexes in the same organism

Hermaphroditism

both male and female reproductive structures in the same organism

Monoecious

either male or female reproductive structures in one organism

Dioecious

What are the sex determining systems?

• Chromosomal

• Genetic

• Environmental

determine the sex of an organism; differ in males and females; X and Y in humans

Sex chromosomes

Chromosomes that are the same in males and females

Autosomes

What are the Chromosomal Sex Determining Systems?

• XX-XO

• XX-XY

• ZW-ZZ

• Haplodiploidy

First studied in grasshoppers

XX-XO Sex-Determination

Explain meiosis in XX-XO sex determination

• Female: all eggs get one X chromosome

• Males: half the sperm get an X chromosome, the other half gets no sex chromosome

sex that produces one type of gametes

Homogametic

sex that produces two types of gametes

Heterogametic

Males and females have the same number of chromosomes

XX-XY Sex-Determination

regions on the X and Y chromosomes allow for pairing during meiosis

Pseudoautosomal

Birds, snakes, butterflies, some amphibians, and fishes

ZZ-ZW Sex-Determination

ZZ

Male

ZW

Female

Bees, wasps, and ants

Haplodiploidy

Haplodiploidy Haploid set

Male

Haplodiploidy Diploid set

Female

No sex chromosomes, only the sex-determining genes; Found in some plants, fungi, protozoans, and fish

Genic Sex-Determining System

Environmental factors like limpet’s position in the stack and temperature in turtles and alligators

Environmental Sex Determination

Turtles: warm temps (>300C)->

Females

Alligators: warm temps ->

Males

The balance (or ratio) of X:A determines

Sex

The X:A stands for

The number of X-chromosomes/the number of haploid sets of autosomal chromosomes

= 1

Female

= 0.5

Male

>1

Metafemale

0.5-1

Intersex

<0.5

Metamale

The importance of the X and Y-chromosomes is demonstrated by the phenotypes that result from abnormal numbers of sex chromosomes:

• Turner Syndrome

• Klinefelter Syndrome

• Jacob’s Syndrome

• Poly-X females

Females with a single X chromosome; 1 in 3000 births

Turner Syndrome

One Y-chromosome and multiple X-chromosomes (XXY is most common)

Klinefelter Syndrome

Two Y-chromosomes and an X-chromosome

Jacob’s Syndrome

Triplo-X syndrome (XXX) most common

Poly-X Females

At least one __ chromosome is needed for human development.

X

The presence of a __ chromosome results in development of the male phenotype.

Y

The absence of a __ chromosome leads to female development

Y

The male determining gene(s) must be located on the __ chromosome.

Y

Extra copies of the __ chromosome often leads to developmental problems in both males and females resulting in physical and mental health problems that increase as the number of __ chromosomes increases.

X

sex determining region on Y

SRY-gene

production > male development

Testosterone

substance > degeneration of female reproductive ducts

Mullerian-inhibiting

An XY individual who appears female, but has an intact SRY gene, may have

Androgen Insensitivity Syndrome

Possessing a single allele at a locus

Hemizygous

Phenotypes determined by genes found on the sex chromosomes

Sex-Linked Characteristics

Hemophilia (reduced blood clotting) is an X-linked recessive disease in humans. A woman with hemophilia mates with a man who exhibits normal blood clotting.

What is the probability that their child will have hemophilia?

1/2

equalizes the amount of expression from X-chromosomes in males and females

Dosage Compensation

The inactive X-chromosome

Barr-body

states that the Barr body is the inactive X-chromosome and that X-inactivation is random so that either X chromosome in any given cell can become the Barr body

Lyon Hypothesis

How is the X-chromosome inactivated?

Xist gene

2/3 of the Y chromosome is

Heterochromatin

How many genes does the Y chromosome encode?

50-60

What is a palindrome?

Sequence that reads the same backwards as forward

one allele completely dominant over another allele

Complete dominance

a heterozygous individual has a phenotype that is intermediate between the two homozygous

Incomplete Dominance

both alleles are expressed in a heterozygous individual

Codominance

I^A and I^B are

Codominant

the percentage of individuals having a particular genotype that express the expected phenotype

Penetrance

when a gene is not always expresses so that the phenotype does not match the genotype in every individual

Incomplete penetrance

the degree to which a trait is expressed

Expressivity

(extra digits) can be inherited as a dominant trait, but it is not always expressed

Polydactyly

causes death at an early stage of development, so some genotypes may not appear among the progeny; Affects the Mendelian genotypic and phenotypic ratios in progeny.

Lethal Alleles

ABO blood types in humans are ____, but they also have ____

codominant; complete dominance

Effects of genes at one locus depend on the presence of genes at other loci.

Gene interaction

How does gene interaction differ from dominance?

• Gene interaction is interaction between genes at different loci.

• Dominance is interaction between alleles at a single locus.

one gene hides (masks) the expression of another gene located at a different locus

Epistasis

the gene that masks

Epistatic gene

the gene that is being masked

Hypostatic gene

Types of Epistasis:

• Recessive

• Dominant

• Duplicate recessive

Recessive Epistasis Ratio

9:3:4

Dominant Epistasis Ratio

12:3:1

Duplicate Recessive Epistasis Ratio

9:7

Turtles and alligators rely on this sex determining system

Environmental Sex Determination

In this sex determining system one or multiple genes dictates the sex of the organism. Common in plants.

Genie Sex Determination

Humans, bees and grasshoppers have this type of sex determination.

Chromosomal Sex Determination

A female grasshopper has the same number of chromosomes as a male grasshopper. True or False

False

In birds, females are the heterogametic sex. True or False

True

Male bees produce gametes by meiotic cell division. True or False

False

In cold temperatures alligator embryos develop as males. True or False

False

A fruitfly with one X chromosome, no Y chromosome and the normal sets of autosomes (2n) will develop as a:

Male

What is the result if the SRY gene on the Y chromosome fails to activate at 6 weeks of development?

The fetus will develop as a female

Bob, who is colorblind, has a child with Sarah, who's father was colorblind. What is the probability that their child with be a boy with colorblindness?

1/4

Sex linked characteristics are

Encoded on a sex chromosome

X-linked alleles are passed from the father to

all his daughters

Who was the fist person to study sex-linked genes in Drosophila?

Thomas Hunt Morgan

A women, who has red-green colorblindness has four sons. What is the probability that all the sons also have red-green colorblindness? Assume normal gamete formation in both the mother and the father.

1

The Xist gene is actively transcribed on the

inactive X-chromosome

What sex-determination system do fruit flies (Drosophila) have?

Genic balance system

The phenotype of the heterozygote is intermediate between the phenotypes of the two homozygotes

Incomplete Dominance

The phenotype of the heterozygote includes the phenotypes of both homozygotes

Codominance

The phenotype of the heterozygotes is the same as the phenotype of one of the homozygotes

Complete Dominance

In epistasis, the _____________gene masks the expression of the ___________________ gene.

Epistatic;hypostatic

Coat color in Labrador Retrievers is determined by two genes exhibiting

Recessive epistasis

Polydactyly is the condition of having extra fingers or toes. Some polydactylous persons possess extra fingers or toes that are fully functional, whereas others possess only a small tag of extra skin. This is an example of

Variable expressivity