Genetics - Chapter 4

Chapter 4 and Quiz 2 Review

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

In sexual reproduction, parents contribute genes to produce an offspring that is genetically distinct from both parents. In most eukaryotes, sexual reproduction consists of meiosis, which produces haploid gametes (or spores), and fertilization, which produces a diploid zygote.

Fertilization Produces?

Produces diploid zygotes

Meiosis Produces?

Haploid gametes

Male Chromosomes are?

XY

Female Chromosomes are?

XX

Define Autosome

The other 22 chromosomes excluding the sex chromosomes

Define Heterogametic

2 different gametes such as XY

Define Homogametic

Same gametes such as XX

How do X and Y chromosomes pair up during meiosis?

X and Y chromosomes pair up due to being homologous in small regions called pseudoautosomal regions

What is a Pseudoautosomal Region?

Areas at the tip of X and Y chromosomes [in humans] with the same gene, allowing for pairing

How does Sex determination in the XX-XY system differ from the ZZ-ZW system?

In the XX-XY system, females are homogametic [ZZ] while males are heterogametic [ZW]

In the ZZ-ZW system, females are heterogametic [ZW] while males are homogametic [ZZ]

How is sex determined?

• Genotypes at one or more loci determine sex

• Sex is determined by genes

  • SYR, located on Y chromosome, determines male phenotype

How can the environment determine sex?

Environmental factors can determine. sex despite possessing sex chromosomes. In species such as turtles, warm temperatures produce females during specific times of year

How is sex determined in fruit flies?

Genetic Balance between Genes on Autosomes and X Chromosomes

Define Genic Balance

Sex in some species is a balance between genes on autosomes and X chromosomes

What is the Fruit Fly Sex ratio?

X : A

When referring to the fly sex ratio, what range can we predict for male fruit flies?

X : A = 0 - 0.5

When referring to the fly sex ratio, what range can we predict for Female fruit flies?

X : A = 1+

How are abnormal numbers of sex chromosomes produced?

Sex chromosomes not properly segregating in meiosis or mitosis

What is Turner Syndrome?

Females lacking 1 X Chromosome

Is it possible to lack both sex cells? [No XX or no XY, just …]

No, embryos missing both sex cells are self aborted

Can males be born without a Y chromosome?

Yes, the Y chromosome does not entirely determine maleness rather the gene on Y chromosome SRY does. XX males are rare but do exist

What is SRY?

• A gene on the Y chromosome that “determines” maleness

• SRY activation causes gonads [undefined private parts] to develop as testes, causing Testerteroone and Mullerian to secrete

• Testosterone causes development of male characteristics

• Mullerian results in the degeneration of female reproductive ducts

What are sex linked characters?

Characteristics determined by genes located on sex chromosomes [X-Linked or Y-Linked]

Define Hemizygous

Only 1 X chromosome so whatever mutation on X chromosome is expressed

If females have 2 copies of every X-Linked gene, how do they not produce 2x the amount of proteins of males?

Dosage compensation - Equalizes the amount protien produced by X-linked genes

Dosage compensation

• Equalizes the amount of protein produced by X-linked genes

• Important so males don’t end up with less protein than women

Give an example of Dosage Compensation

Male fruit flies double the activity of X linked traits

Define Bar Body

In each female cell, ALL but 1 X chromosome is randomly deactivated

Explain how women are functionally hemizygous for X-linked genes

In heterozygous women for example, 50% of cells express 1 Allele and the other 50% express the other 1 Allele

Give the Genotype for a Female with Turner Syndrome

X / XO

Given the following description, provide the genotype: Biologically male but the karyotype indicated the presence of only X chromosomes

XX with SRY on X

What is Klinefelter syndrome?

Males are born with one or more Y chromosomes and several X Chromosomes

The following Genotypes indicate which syndrome? XXY, XXXY, XXYY

Klinefelter syndrome

Klinefelter syndrome affects?

Males and symptoms include sterile, little hair, and very tall

What is Poly-X Syndrome?

Biologically Female with an over expression of X Chromosomes

A person with the following genotype most likely has which syndrome? XXX, XXXX

Poly-X Syndrome

What symptoms would a person with Poly-X Syndrome have?

Female, tall and thin

Y-linked traits can only be passed from _____ to ___

Y-linked traits can only be passed from biological father to son

Which statements describe Y‑linked traits?

(A) The phenotype is solely expressed in males.

(B) Male offspring of a female with the phenotype will also express the phenotype.

(C) Females have a greater probability of being a carrier of the trait.

(D) The trait is passed down to a son by his biological father.

(E) A male with the trait will pass the trait to 100% of his female offspring.

A, D

Do X and Y Chromosomes play a role in sex determination in fruit flies?

No, the ratio of X chromosomes to the number of haploid autosome sets determines fly sex

When will a fruit fly be Female?

When the ratio is 1.0

When will a fruit fly be Male?

When the ratio is 0.5

When will a fruit fly be Metafemale?

When the ratio is greater than 1

When will a fruit fly be Metamale

When the ratio is less than 0.5

When will a fruit fly be intersex?

When the ratio is 0.5 - 1.0

In fruit flies, what determines if a male fly will be sterile?

Any male who lacks a Y chromosome will be sterile

Imagine you are asked to calculate the sex phenotype of fruit flies given various Autosomal Chromosome sets. How many sets do you have in

(A) Normal

(B) 4 Haploid Sets

(C) 3 Haploid Sets

(A) 2

(B) 4

(C) 3

What is the Sexual phenotype for a XX fly with 4 haploid sets of autosomes

2:4, sterile male

• A fly that is XX with four haploid sets of autosomes has twice as many autosomes as a normal fly. Therefore, the ratio of X to autosomes is 2:4, or 0.5, and the fly will be a sterile male.

What is the Sexual phenotype for an XXX fly with 3 haploid sets of autosomes?

3:3, Female

• A fly that is XXX with three haploid sets has a ratio of 3:3, or 1, and will thus be female

What is the Sexual phenotype for an XXY fly with a normal haploid set of autosomes?

2:2, Female

A normal female Drosophila produces abnormal eggs that contain a complete diploid set of her chromosomes. She mates with a normal male Drosophila that produces normal sperm.

What will the sex ratio of the progeny from this cross be?

(A) 50% males, 50% females

(B) 50% female, 50% metafemale

(C) All females

(D) 50% female, 50% intersex

(E) 25% male, 50% intersex, 25% female

D

n-Drosophila melanogaster, the level of expression of genes on the X chromosome in males is doubled.

What phenomenon is this an example of?

1. Dosage compensation

2. genomic imprinting

3. extranuclear inheritance

4. paternal mitochondrial leakage

1. Dosage compensation

What is the Xist gene?

On an X chromosome destined to be inactivated, the Xist gene is produced, producing a long RNA molecule that coats the X chromosome and inactivates the genes on it by recruiting protein complexes to alter chromatin structure

When does X inactivation occur?

During gastrulation, the embryo begins to differentiate into distinct cell lineages

What is Gastrulation?

When the embryo begins to differentiate into distinct cell lineages. X inactivation also occurs

After fertilization of the mature oocyte, the single cell female embryo is ____, meaning?

Diploid, it has yet to undergo X inactivation. Therefore, 2 non-silenced copies of the allele are present.

What does it mean to be diploid?

2 sets of each chromosome [23 coming from mom, 23 from dad]

What does it mean to be Haploid?

one set

How many chromosomes are in Haploid individuals?

23

Haploid =

n

How many chromosomes are in diploid individuals?

46

Diploid = 2()

2n

Hemophilia is called "the royal disease" because many European royal families had members with the condition. Hemophilia is a recessive, X‑linked condition. Queen Victoria was unaffected by hemophilia but was a carrier of the hemophilia gene (X^HX^h). Suppose Queen Victoria's husband, Prince Albert, had hemophilia (X^hY).

What is the percent probability that a son of Queen Victoria and Prince Albert would not have hemophilia?

50%

Hemophilia is called "the royal disease" because many European royal families had members with the condition. Hemophilia is a recessive, X‑linked condition. Queen Victoria was unaffected by hemophilia but was a carrier of the hemophilia gene (X^HX^h). Suppose Queen Victoria's husband, Prince Albert, had hemophilia (X^hY).

What is the percent probability that a daughter or son of Queen Victoria and Prince Albert would have hemophilia?

50%

Hemophilia is called "the royal disease" because many European royal families had members with the condition. Hemophilia is a recessive, X‑linked condition. Queen Victoria was unaffected by hemophilia but was a carrier of the hemophilia gene (X^HX^h). Suppose Queen Victoria's husband, Prince Albert, had hemophilia (X^hY).

Probability of one son with hemophilia and then one daughter with hemophilia:

6.25%

¼ x ¼ x 100 = 6.25%

Red–green color blindness is an X‑linked recessive trait in humans. Polydactyly (extra fingers and toes) is an autosomal dominant trait. Martha has wild‑type fingers and toes and color vision. Her biological mother is wild‑type in all respects, and her biological father is color blind and has polydactyly. Bill is color blind and has polydactyly. His biological mother has color vision and wild‑type fingers and toes.

When answering the given question, consider that the answers include the proportions of only some of the possible phenotypes; other phenotypes are also expected to occur but are not included.

If Bill and Martha have children together, what proportions of children with specific phenotypes would they be expected to produce?

1/8 color‑blind daughters with polydactyly, 1/8 sons with color vision and wild‑type fingers

What is the haploid number of chromosomes for humans?

n = 23

What is the haploid number of chromosomes for humans?

2n = 46

For a human, 2n = 46 How many chromosomes and pieces of DNA do we have in PROPHASE I

Chromosomes = 46

DNA = 92

For a human, n = 23 How many chromosomes and pieces of DNA do we have in PROPHASE II

Chromosomes = 23

DNA = 46

Meiosis I is often referred to as the?

Reduction Division

Given 2n = 46 how many chromosomes and DNA are in Prophase I?

Chromosomes = 46

DNA = 92

Given 2n = 46 how many chromosomes and DNA are in Metaphase I?

Chromosomes = 46

DNA = 92

Given 2n = 46, how many chromosomes and DNA are in Anaphase I?

Chromosomes = 46

DNA = 92

Given 2n = 46, how many chromosomes and DNA are in Telophase I?

Chromosomes = 46

DNA = 92

Given 2n = 46, how many chromosomes and how much DNA are in Cytokinesis I?

Chromosomes = 23

DNA = 46

Meiosis 2 is called the?

Equal Division

Given 2n = 46, how many chromosomes and how much DNA are in Prophase II?

Chromosomes = 23

DNA = 46

Given 2n = 46, how many chromosomes and how much DNA are in Metaphase II?

Chromosomes = 23

DNA = 46

Given 2n = 46, how many chromosomes and how much DNA are in Anaphase II?

Chromosomes = 46

DNA = 46

Given 2n = 46, how many chromosomes and how much DNA are in Telophase II?

Chromosomes = 46

DNA = 46

Given 2n = 46, how many chromosomes and how much DNA are in Cytokinesis II?

Chromosomes = 23

DNA = 23

Why don’t cells re-enter interphase before Meiosis II?

In Meiosis I, DNA has been copied 1x. If interphase happened again, we’d replicate the DNA again, ending up with extra copies of DNA in our gametes

What is the rule for X-Linked Dominant traits?

Affected daughters come from affected fathers

What is the rule for X-Linked recessive traits?

Affected sons come from affected mothers

What is the Geneic Balance ratio for fruit flies?

X:A

What is the sex of a fruit fly with XXX and 3 sets of haploid autosomes?

Female, 3:3

What is the goal of Meiosis?

The goal oof meiosis is to make 4 genetically different gametes [sex cells]

What’s the acronym for remembering the stages of Meiosis?

PMAT x2

What happens in S-Phase [Meiosis]?

DNA replicates

What happens in Prophase I?

• Nuclear envelope disappears

• Chromatin condenses into chromosomes

• Homologous pairs of chromosomes pair and line up next to each other

• Crossing over occurs

What is crossover, and when does it occur?

• Prophase I

• Paired chromosomes exchange segments of DNA, creating genetic diversity

What is Metaphase I?

• Homologous pairs of chromosomes line up in the middle

What is Anaphase I

Homologous pairs separate moving towards opposite spindle poles

What is telophase I?

• Chromosomes arrive at the spindle poles

• Nucleus regrows

• Chromosomes unwind back into chromatin

What is cytokinesis I

Cytoplasm divides the cell into 2

What is the result of Meiosis I?

• Cell divides into 2 haploid cells

• The 2 cells each contain ½ the original number of chromosomes and DNA

What happens in Prophase II?

• Chromosomes condense

• The nuclear envelope dissolves

What happens in Metaphase II?

• Chromosomes line up in the middle