Exam 4 - Meiosis and Inheritance (28)

Why did Mendel succeed with his genetic research? (3)

1. chose pea plants that are easy to cross
2. chose obvious and distinct traits like color/shape
3. used homozygous lines

what are homologous chromosomes

chromosomes with the same gene, one from each parent.

are homologous chromosomes exactly the same? if not what makes them different

no, they might have different alleles for the same gene

what is ploidy

number of copies of each chromosome

what kind of ploidy are we

diploid (2n, 2 copies of each chromosome, one from each parent)

what type of ploidy are our gametes and what type are our somatic cells

gametes are haploid, somatic are diploid

how do haploid gametes form?

meiosis

what is the main purpose of mitosis

to grow and produce more somatic cells, keep the 2n

what is the main purpose of meiosis

creation of sperm and egg cells

how is a zygote formed

sperm and egg cell combine

how is the beginning of mitosis and meiosis similar

they both have to replicate chromosomes in a 2n cell.

how many chromosomes in a 2n cell

46 sticks (23 types of chromosomes)

how many chromosomes after replication stage early

46 chromosomes, this time each w 2 sister chromatids

how many gametes are formed after meiosis

4

what is the ploidy after homologs separate

n

how many chromosomes after homologs seperate

23

what is the ploidy after sister chromatids separate

n

how many chromosomes after sister chromatids separate

23

what is the most similar step of meiosis to mitosis, other than dna replication

meiosis 2 when sister chromatids separate --> similar to mitosis

what is the principle of segregation

2 alleles for a gene separate during meiosis and are segregated evenly into gametes

how many alleles of a gene do we have

2

how many alleles of a gene do we pass down to our kids

1

during which step of meiosis are pairs of alleles separated

meiosis I when homologs separate

what is the principle of independent assortment

genes that aren't on the same chromosomes assort independently from each other. So the dominant R allele chromosome can be sorted separatley from a dominant Y allele,

during what stpe of meiosis do genes assort independently

meiosis 1 when homologus split but can be lined up in different ways

what does independent assortment do

generate genetic diversity --> mixes up which alleles end up in which gametes

what is the formula to figure out the possible different gametes if there are 2 alleles per gene

2^x.
x = haploid chomosome number.
ex. 2^23 for humans

what is nondisjunction

failure to separate chromosomes correctly in either meiosis I or II

what happens if nondisjunction happens in meiosis 1

homologs did not happen so one of the 2 resulting cells has 2 copies of the same chromosome instead of 1.

what happens if nondisjunction happens in meiosis II

one or more of the gametes would be missing an allele since sister chromatids would not split and both copies of the same allele would end up in one gamete and not another gamete.

what can result if nondisjunction

aneuploidies

what is an aneuploidies

abnormal number of chromosomes. gametes have too little or too much chromosomes

what is down syndrome

trisomy 21, caused by nondisjunction that results in 3 copies of chromosome 21

explain specifically what happened with egg and sperm for down syndorme to happen. (pretend egg is wonky)

egg went through nondisjunction which resulted in it having an extra copy of chromosome 21. sperm has normal amt of chromosome 21, 1 copy. sperm and egg fertilize together and creates zygote with 3 copies of chromosome 21