AP Bio Unit 5

Meiosis

a process that ensures the formation of haploid (n) gamete cells in sexually reproducing diploid (2n) organisms

half

Meiosis results in daughter cells with ______ the number of chromosomes of the parent cell. 

two

Meiosis involves ____ rounds of a sequential series of steps:

Meiosis I

separates homologous chromosomes (two  chromosomes in a pair, one from mother and one from father)

Meiosis II

separates sister chromatids

prophase I

the chromosomes condense, and the nuclear envelope breaks down. Crossing-over occurs

metaphase I

pairs of homologous chromosomes move to the equator of the cell

anaphase I

homologous chromosomes move to the opposite poles of the cell

telophase I and cytokinesis

chromosomes gather at the poles of the cell. the cytoplasm divides (into 2 cells)

n

set of chromosomes

haploid (n)

1 set

| |

diploid (2n)

2 sets

||

number of cells produced and the genetic content of the daughter cells

Mitosis and meiosis are similar in the way chromosomes segregate but differ here.

prophase II

a new spindle forms around the chromosomes (2 cells)

metaphase II

chromosomes line up at the equator (2 cells)

anaphase II

centromeres divide. chromatids move to opposite poles of the (2) cell(s)

telophase II and cytokinesis

a nuclear envelope forms around each set of chromosomes. the cytoplasm divides (into 4 cells)

Mitosis vs. Meiosis

2 genetically identical cells vs 4 different cells

8\.4 million

2²³ (2^n); number of possible combinations of chromosomes

Separation of the homologous chromosomes in meiosis I

ensures that each gamete receives a haploid (1n) set of chromosomes that comprises both maternal and paternal chromosomes. 

crossing over

During meiosis I, homologous chromatids exchange genetic material via this process, which increases genetic diversity among the resultant gametes. 

crossing over, the random assortment of chromosomes during meiosis, and subsequent fertilization of gametes

Sexual reproduction in eukaryotes involving gamete formation—serves to increase variation. 

random assortment

independent; homologous pairs line up independent of each other in metaphase I

genetic variation

Crossing over, independent assortment of chromosomes, segregation, and fertilization result in this in populations. 

segregation

separation of chromosomes in anaphase

pattern of transmission of genes

The chromosomal basis of inheritance provides an understanding of this from parent to offspring. 

certain human genetic disorders

can be attributed to the inheritance of a single affected or mutated allele or specific chromosomal changes, such as nondisjunction.

nondisjunction

failure of chromosomes to separate

normal meiosis

2n=4 → n=2

nondisjunction in meiosis I

homologous chromosomes don’t separate

n+1, n+1, n-1, n-1

nondisjunction in meiosis II

sisters don’t separate

n+1, n-1, n, n

DNA and RNA

carriers of genetic information. 

ribosomes

found in all forms of life

Major features of the genetic code

shared by all modern living systems. 

Core metabolic pathways

conserved across all currently recognized domains.

Mendel’s laws of segregation and independent assortment

can be applied to genes that are on different chromosomes.

Law of segregation

separation of genes/alleles

homozygous

true-breeding

3:1

ratio of phenotypes when two heterozygous cross according to Mendelian Genetics

9:3:3:1

ratio when two heterozygous cross in a dihybrid cross (two traits) according to Mendelian Genetics

allele

different versions of a gene

Fertilization

involves the fusion of two haploid gametes, restoring the diploid number of chromosomes and increasing genetic variation in populations by creating new combinations of alleles in the zygote

Rules of probability

can be applied to analyze passage of single-gene traits from parent to offspring. 

the pattern of inheritance

(monohybrid, dihybrid, sex-linked, and genetically linked genes) can often be predicted from data, including pedigree, that give the parent genotype/phenotype and the offspring genotypes/phenotypes.

Laws of Probability

If A and B are mutually exclusive, then: P(A or B) = P(A) + P(B) 

If A and B are independent, then: P(A and B) = P(A) × P(B)

A and a

dominant and recessive allele, respectively

phenotype

physical trait (purple or white)

genotype

genetic makeup (AA/Aa/aa)

homozygous dominant

AA (same allele)

homozygous recessive

aa (same allele)

heterozygous

different alleles (Aa)

environmental factors

influence gene expression and can lead to phenotypic plasticity.

Phenotypic plasticity

occurs when individuals with the same genotype exhibit different phenotypes in different environments.

Arctic Fox and Phenotypic Plasticity

In the summer, the Arctic fox can hide better in the brown trees and the bare ground. In the winter, the fox can camouflage in the snow as a white fox. Their fur color is a protective adaptation so they can hide from predators and sneak up on prey.

American Peppered Moth Caterpillars and Phenotypic Plasticity

The caterpillar can blend in with brown twigs if it is brown to prevent predators from finding it. It can be green to camouflage with green twigs.

Daphnia and Phenotypic Plasticity

The Daphnia can swim faster with longer helmets and tail spines, and it can escape its predators easier. They can protect and defend themselves from the detected predators in the area. The protection, however, is only when predators are present, because it takes too much energy if the protection was year round.

Plant Stomata and Phenotypic Plasticity

more stomata → more CO2 absorbed to keep the plant alive in low CO2 concentrations

less stomata → store CO2 for longer because there is a lot of excess CO2 in the air

autosomes

chromosome pairs 1-22

sex chromosomes

chromosome pair 23

Rr

carrier of recessive (disease-causing) gene

different phenotypes

same genotype in different environment

Nature vs. Nurture

Nature: deals the cards (genetics)

Nurture: plays the hand (environment)

Patterns of inheritance of many traits

do not follow ratios predicted by Mendel’s laws and can be identified by quantitative analysis, where observed phenotypic ratios statistically differ from the predicted ratios

complete dominance

Mendelian -- AA x aa → Law of Independent Assortment

codominance

both traits expressed; example: blood type

A allele - IA; B allele - IB; O allele - i

A blood: IA IA, IA i

B blood: IB IB, IB i

AB blood: IA IB

O blood: ii

incomplete dominance

blend of traits

red + white flowers => neither dominant => pint or spotted offspring

linked genes

Law of Dependent Assortment; observed numbers do not match the expected; if genes are like this, majority of offspring resemble parents

sex-linked, polygenic inheritance, and non-nuclear

other types of genetics that do not follow Mendel’s laws

genetically linked

a. Genes that are adjacent and close to one another on the same chromosome may appear to be_________________

map distance

the probability that genetically linked genes will segregate as a unit can be used to calculate this between them. 

further

b. The ___________ the distance between genes, the more likely crossing over will occur.

sex-linked traits

determined by genes on sex chromosomes; The pattern of inheritance of these can often be predicted from data, including pedigree, indicating the parent genotype/phenotype and the offspring genotypes/phenotypes. 

polygenic inheritance

Many traits are the product of multiple genes and/or physiological processes acting in combination; these traits therefore do not segregate in Mendelian patterns.

non-nuclear inheritance

chloroplast and mitochondria DNA

Chloroplasts and mitochondria

are randomly assorted to gametes and daughter cells; thus, traits determined by their own DNA do not follow simple Mendelian rules

egg; sperm; maternally

in animals, mitochondria are transmitted by the __ and not by

ovule; pollen; maternally

c. In plants, mitochondria and chloroplasts are transmitted in the _____ and not in the _______;__ as such, mitochondria-determined and  chloroplast-determined traits are ____________inherited.

recombination frequency

recombinants/total offspring x 100 = % = map units

recombinant

ex: AaBb x aabb → Aabb or aaBb (different from parent)

null hypothesis

Mendel’s Law of Independent Assortment -- unlinked genes

AaBb x aabb → AB aB Ab ab → expected 1:1:1:1

alternative hypothesis

Linked genes -- non-Mendelian -- observed and expected differ greatly

mutliply

AND probability

AA and aa

1/4 \* 1/4 = 1/16

add

OR probability

AA or aa

1/4 + 1/4 = 1/2

unlinked

AaBb → AB Ab ab ab

linked

AaBb → AB ab - no crossing over, meaning lower chance of genetic diversity

difference between nuclear DNA and mitochondrial DNA

nuclear: mom and dad

mitochondrial: just mom

crossing over and independent assortment

ways meiosis produces genetic variation

advantages: everyone’s different, natural selection + evolution

segregation

chromosomes separate

BADC

A-B 15%

B-C 45%

B-D 40%

A-D 25%

what is the order of genes?

skips generation

this means that the trait is MOST LIKELY recessive

more males

this means the trait is MOST LIKLEY sex linked

purpose of meiosis

human 46 chromosomes → after meiosis 23 → combine with other parent → keep @ 46