Final exam review

Chromatin

granular material visible within the nucleus; consists of DNA tightly coiled around proteins

Chromosomes

threadlike structures made of DNA molecules that contain the genes

Alleles

alternative versions of a gene

The chromosomal theory of inheritance states that

genes are on chromosomes and carry genetic information

Chromosomes come in ______ and are separated in ________

pairs; meiosis

We each have __chromosomes on each cell, __ pairs

23, 46

Formula for a diploid cell

2N=46

What does meiosis generate?

haploid gametes (1n) and enhances genetic variation

synapsis

the pairing of homologous chromosomes during meiosis

What kind of cell does meiosis begin with?

Diploid

recombination

a combining of genes or characters different from what they were in the parents

What does meiosis 1 do?

reduces haploid number from 2n to 1n

Describe the major events of Prophase 1

homologous chromosomes pair up forming bivalent sister chromatids, synapsis gives rise to a tetrad with overlapping of nonsister chromatids, Nuclear envelope and nucleolus break down, and the two centromeres of the tetrad attach to the spindle fibers

tetrad

two pairs of sister chromatids

chiasma

nonsister chromatids

What structure is responsible for crossing over?

The Synaptonemal Complex

Describe anaphase 1

half of each tetrad is randomly pulled (disjunction) to opposite poles

Describe the beginning of Meiosis 2

No DNA replication before Meisosis 2
Sister chromatids separate
Each gamete has one chromatid from each pair of homologous chromosomes

Prophase 2

chromosomes are made up of a pair of sister chromatids connected by a centromere

Metaphase 2

centromere is positioned at the metaphase plate

Anaphase 2

Centromeres divide and sister chromatids are pulled to opposite poles

Telophase 2

cytokinesis results in 4 haploid gametes with equal cytoplasm

Describe the product of meiosis 2

4 haploid cells have different combos of maternal and paternal genes

describe the divisions that take place in Meiosis 1 and 2

First division, reductive; second division, equatorial

Describe the similarities and differences between meiosis and mitosis

Pairing up does not happen in mitosis
Meiosis I is a reductional division with the same steps as mitosis, but reduces ploidy
Meisosis 1: After Prophase I, steps similar to mitosis occur but the behavior of chromosomes/chromatids is different in MI.

Ploidy

haploid number

What kind of meiotic mistake is down syndrome? on which chromosome?

trisomy on the 23rd chromosome

Meisosis reduces the chromosome number by half; diploid number is then restored by

fertilization

Describe Mendels four postulates of genetics

1. Each trait is controlled by a pair of factors (genes)
2. When 2 different factors for a trait are present in an individual and one is dominant and the other is recessive
3. During gamete formation the paired factors segregate randomly
4. During gamete formation segregating pairs of unit factors assort independently

What law can be used to calculate frequencies of F2 phenotypes?

Product Law

Describe the Product Law

when 2 independent events occur simultaneously the outcome is the 2 probabilities multiplied by each other

A test cross always uses

homozygous recessive genotype

In a trihybridcross, what genotypic ration do two heterozygotes create

1:1:1:1

formula to find # of types of gametes formed

2^n, where n = the # of heterozygous gene pairs

formula to find # of different genotypes

3^n, where n = the # of heterozygous gene pairs

formula to find # of different phenotypes

2^n, where n = the # of heterozygous gene pairs, assuming a simple dominant/recessive relationship

Proband

the individual displaying the trait or characteristic being studied

What is the default assumption in a pedigree?

homozygous normal

What kind of mutation is albinism?

Recessive

What kind of mutation is Huntingtons disease?

Lethal Dominant

What kind of disease is cystic fibrosis?

autosomal recessive

Most common genetic defect in caucasians

cystic fibrosis

What is the sum law used for?

Finding the probability of an event which can occur through 2 or more combinations of independent events

How do you use the Sum Law?

Find all possible combinations, the probability of each event, then the probability of each combo, and add together the probability of all possible combos

degrees of freedom (df)

n-1, where n is the number of categories

Chi-square formula

(observed-expected)^2/expected

What is the Chi-square test?

checks whether a distribution is significantly different than an expected or theoretical distribution

What does it mean to fail to reject the null hypothesis?

There is no real difference between the data; any difference is due to chance

What does it mean to reject the null hypothesis?

That it is very unlikely that the difference between the groups is due to chance

incomplete dominance

neither allele is completely dominant over the other, heterozygote has an intermediate phenotype

Codominance

distinct expression of gene products from both alleles

Why can multiple alleles only be studied in populations?

Individuals only have 2 alleles for a given gene

What mode of inheritance is the ABO system?

codominance

dominant lethal allele

presence of one copy of allele results in death

recessive lethal allele

an allele that prevents the birth or survival of homozygotes

pleiotropy

A single gene having multiple effects on an individuals phenotype

If there are four possible phenotypes, how many genes are there?

1

If there are 16 possible phenotypes, how many genes are there?

2

If there are 64 possible phenotypes, how many genes are there?

3

epigenesis

each step of development increases the complexity of the organ or feature of interest and is under the control and influence of many genes

antagonistic effect

masking

epistatic

the gene that does the masking

hypostatic

gene that is masked

phenotypic ration that indicates recessive epistasis

9:3:4

phenotypic ratio that indicates dominant epistasis

12:3:1

complementary gene interaction

two different genes that work together to create a specific phenotype

complementary gene interaction phenotypic ratio

9:7

complementation analysis

used to determine if two mutations causing a similar phenotype are alleles of the same gene or on two separate genes

in complementation analysis, what genotypes are crossed?

two mutant strains

in complementation analysis, what does one normal copy of each gene indicate?

complementation occurs and the alleles are on separate genes

in complementation analysis, what does 1 gene that is mutant in all cases and a second normal gene indicate

no complementation, the alleles are on the same gene

penetrance

percentage of individuals that express a gene out of individuals who have the gene

expressivity

The range of expression of a gene

genetic anticipation

genetic disorders that worsen as they are passed through generations

linkage

when 2 traits are located on the same gene

Which traits have crisscross inheritance patterns?

sex linked traits

sex limited

autosomal genes expressed only in one sex

sex influenced

expression of a trait is influenced by sex but not limited to one sex or the other

extranuclear inheritance

the inheritance of genetic material that is not found within the nucleus

do genes found outside the nucleus follow mendelian laws of genetics

no

maternal effect

phenotype determined by information maternal gamete

Supermale

male with an extra Y chromosome

Superfemale

female with an extra X chromosome

Hermaphrodite

have both male and female genitalia

Barr bodies

inactivated female chromosome

XY/XX system

Heterozygotes are male, homozygotes are female (humans)

XO/XX system

2 Xs is female, one is male (insects)

ZW/ZZ system

males are the homozygote, females are the heterozygote

Temperature Dependent Sex Determination

believed to involve steroids

Genetic Balance Theory

instead of XY chromosomes, sex is determined by the genic balance or ratio between X

SRY

Sex determining region
Not expressed: gonads become ovaries
Expressed: gonads become testis

MSY

Male specific region of the Y chromosome

TSD

Testis determining factor

XX Males

have the SRY on the X chromosome

XY females

missing SRY gene

The Lyon Hypothesis

Inactivation of female X chromosomes is random

N

1 rule

Klinfelter syndrome

Males with multiple X's

Turner syndrome

Females w only one X

What causes Klinefelter syndrome and Turner syndrome?

Nondisjunction