Unit 4 - Meiosis and Genetics

Question 1

Meiosis

Answer 1

the only function of meiosis is to produce haploid gametes (egg or sperm)

sexual reproduction:
- egg and sperm come together
- offspring are not identitical to parent or to each other

**you start with one 2n cell (diploid) and then get 4 haploid cells (1n)

Question 2

Prokaryotes Reproduction

Answer 2

prokaryotes reproduce by binary fission (asexual reproduction)
- no egg or sperm needed
- the offspring are identitical to the parent

Question 3

Eukaryotes reproduction by mitosis/cytokenesis

Answer 3

• for them, asexual reproduction, you just can chop off part of their body and it will regrow

ex: planaria
- chop it in half and the halves will regrow to be one whole planaria

Question 4

The Sexual Life Cycle of Animals

Answer 4

• you start with 2 diploid parents and their egg and sperm mix for fertilization

fertilization – you get a haploid cell from the egg and a haploid cell from the sperm
- egg and sperm come together

mitosis – the 2n zygote (diploid) goes through mitosis to make a bunch of daughter cells to become a human

**Gamete formation (meiosis), fertilization, growth (mitosis) and development (your growing somatic cells)

Question 5

Homologous Chromosomes

Answer 5

you get one chromosome from mom and one chromosome from dad

• each chromosome has 2 sister chromatids together
• they always have the same genes in the same location
• separate during anaphase of meiosis 2
• are held together by cohesins
• cross over during prophase 1

Question 6

Sex Chromosomes

Answer 6

a pair of chromosomes that determine the person’s sex

XX = female
XY= male

• the X chromosome is bigger than the Y chromosome

Question 7

Autosomes

Answer 7

chromosomes that aren’t sex chromosomes

• every chromosome except the sex chromosome that determines the person’s sex

Question 8

Allele

Answer 8

a variant or version of a specific gene
- so each gene can have multiple versions (alleles) that can be inherited

– the same gene can have different alleles
ex: the fur color locus could either be black or yellow of a gene giving the organism different fur colors

ex: which allele will be inherited if mom = straight hair and dad = wavy hair

Question 9

Meiotic Cell Cycle

Answer 9

G1 = start with diploid cell

S = DNA Replication

G2 = centrosomes appear

Meiosis 1 = diploid cell
- prophase I
- metaphase I
- Anaphase I
- Telophase I
Cystokinesis

then after Meiosis 1, they go thru the Meiosis II

Meiosis 2: start with 2 haploid cells and end with 4 haploid cells

• prophase 2
• metaphase 2
• Anaphase 2
• Telophase 2
• Cytokinesis 2

Question 10

Meiosis: Prophase 1

Answer 10

• chromosomes condense
• nuclear envelope breaks into fragments
• centrosomes move
• meiotic spindle forms (microtubules grow out of it)
  *all of this is the same as prophase in Mitosis

new stuff:
- synapsis occurs – pairing of homologous chromosomes
ex: dad’s chromosome #1 and mom’s chromosome #1 pair up
- have synaptonemal complex

• Crossing over – exchange of genetic material between non-sister chromatids
• (the chromosome crosses over with a diff. chromosome) – think blue and red chromosomes and now they’re partially red and partially blue

Question 11

Synaptonemal Complex

Answer 11

the protein between the homologous chromosomes (holds them together)

• looks like little hairs
• layered on top of each other

Question 12

After Crossing Over happens we get…

Answer 12

Recombinant chromatids
- new combination of alleles
- we have recombinant chromatids after crossing over happens in meiosis

non-recombinant chromatids
- have not exchanged genetic material
- chromosomes that are completely paternal or maternal

• same amount of chromosomes still that you had from beginning

Question 13

Meiosis: Metaphase 1

Answer 13

• the homologous pairs align on metaphase plate randomly
  random alignment = independent assortment
  ex: blue chromosome next to red chromosome
• same amount of chromosomes still that you had from beginning

Question 14

Meiosis: Anaphase 1

Answer 14

• homologous pairs separate from each other (move to opposite sides of the cel)
• kinetichore microtubules shorten
• synaptonemal complex degrades
• sister chromatids stay attached
• non-kinetichore microtubules lengthen and the cell elongates

Question 15

Meiosis: Telophase and Cytokinesis

Answer 15

same as mitosis:
- chromosomes decondense (uncondensing)
- nuclear envelope reforms
- centrosomes and spindle disappear
- cleavage furrow happens

result from meiosis 1:
- 2 daughter cells that are haploid
- each chromosome has 2 sister chromatids

Question 16

Meiosis: Interkinesis

Answer 16

interkinesis happens in between cell divisions (in between meiosis 1 and meiosis 2)
- DNA Replication doesn’t occur again (not going thru the cell cycle again bc we want to end with haploid cells)

**now both daughter cells will enter Meiosis 2

Question 17

Meiosis: Prophase 2

Answer 17

• chromosomes condense
• DNA becomes tightly packed
• nuclear envelope degrades
• centrosomes move to opposite sides of the cell
• mitotic spindle forms

Question 18

Meiosis: Metaphase 2

Answer 18

chromosomes aligned on metaphase plate
- random alignment on the plate

Question 19

Meiosis: Anaphase 2

Answer 19

sister chromatids separate
- they move to opposite sides of the cell

Question 20

Meiosis: Telophase 2 and Cytokinesis

Answer 20

chromosomes decondense (they get bigger and look like strings)
- nuclei reform

result:
- end up with 4 haploid daughter cells

Question 21

Genetic Variation in Offspring due to:

Answer 21

1. Mutation - can happen during cell cycle, DNA replication…
2. Random alignment of chromosomes on metaphase 1 plate

• humans can produce 2^23 different gametes

3. Crossing Over
4. Fertilization - random
   - you would have a 1 in 7 trillion chance of having the same as your sibling

Question 22

Non-disjunction

Answer 22

homologous chromosomes or sister chromatids don’t separate from each other
- whenever DNA is supposed to separate and it doesn’t

**you end up with aneuploid gametes (mistaken # of chromosomes - either n+1 or n-1)

Question 23

Trisomy

Answer 23

when you get an extra chromosome (n +1)

ex: Chromosome 21 - Down Syndrome
- can’t have trisomy 1 bc there’s so many genes that chromosomes
- the older the mom is, the more of a chance she is at to have a baby with downs

**you have extra genes but would have a lot of phenotypic differences

Question 24

Monosomy

Answer 24

when you have n - 1
- only one chromosome

ex: Turner’s Syndrome
- people with Turner’s syndrome can survive
- they only have one sex chromosome (not a lot of info on the Y chromosome)

**hard to survive as a monosomy bc you’re missing a lot of genes if you’re missing an entire chromosome

Question 25

Maternal Age and Down Syndrome

Answer 25

as maternal age increases, the risk of an anaplode increases - this increases bc when you're a fetus, you're eggs go thru meiosis (if you're 20, you're eggs have been sitting thru for 20 yrs) - as you get older, it's more likely that you ignore metaphase check point

Question 26

Blending Inheritance

Answer 26

The original hypothesis for genetics - this is not right - they thought that if you had a black animal and a white animal their offspring would be gray

Question 27

Particulate Inheritance

Answer 27

inheritance of particles - medel prevented self-fertilization by brushing pollen from one flower plant onto another (bred them together) ex: blue and yellow paints and you get either yellow or blue

Question 28

The Pea as a Model Organism

Answer 28

- it's a good model organism - easy to see traits --> you can easily see what trait the offspring inherited from the parents - controlled matings (you can pick which flower mates with which flower) - can produce many offspring - short generation time - generation time = an individual being born to when it can reproduce - for peas it's just a couple of months -- other info: - pea plants can self-fertilize

Question 29

Generations

Answer 29

1. True-breeding plants - (P) Parental Generation (they're homozygous) 2. First Generation (F1) - one trait seen dominant = the trait seen in F1 - one trait hidden recessive = can't see this trait in F1 3. Second Generation (F2) - two F1s are crossed to get an F2 alleles played into this - ex: a gene encoding for flower color - there will be a purple allele and a white allele

Question 30

Genotype vs. Phenotype

Answer 30

ex: Purple flower color Genotype: the genes - Pp Phenotype: physical characteristics - Purple flower color **Phenotype is determined by the Genotype - look to see what alleles they have and then what trait the offspring will inherit

Question 31

Mendel's Law of Segregation

Answer 31

genes that come in pairs separate from one another during the formation of gametes - the law is talking about the separation of homologous chromosomes during anaphase 1 of meiosis

Question 32

Homozygous Dominant

Answer 32

the same alleles and they are both dominant ex: purple flower color PP

Question 33

Heterozygous

Answer 33

2 different alleles ex: purple flower color Pp - still inherit the dominant trait because the flower has half of the amount of enzyme to make the flower color purple which is enough

Question 34

Homozygous Recessive

Answer 34

2 same alleles - both recessive alleles (little ones) ex: purple flower color pp - neither allele has the enzyme that makes the purple pigment which is why you would get a white flower

Question 35

Autosomal Recessive

Answer 35

the gene is not on a sex chromosome - you need 2 mutated alleles for the phenotype to be seen ex: Cystic Fibrosis - mutations in CFTR gene, they can have cystic fibrosis - it's a recessive autosomal disease

Question 36

Carrier (for a condition or trait)

Answer 36

carrier = the person is heterozygous - they have a mutated allele but they don't show the condition - they can pass on the trait to their offspring ex: Pp

Question 37

Inheritance of Dominant Traits

Answer 37

- if you have a dominant trait that doesn't mean it's common - usually one affected parent autosomal dominant: - only need one mutated allele (if recessive, need 2 mutated alleles)

Question 38

Pedigrees

Answer 38

pedigrees = genetic term for family tree circles = female squares = male - if the circle or square is filled in, that means that person has the trait **if you see only one shape filled in (usually squares) that means the trait is sex-linked

Question 39

Independent Assortment

Answer 39

each pair of alleles segregates independently -- of any other pair of alleles -- during gamete formation **this occurs during Metaphase 1 of Meiosis

Question 40

Incomplete Dominance

Answer 40

when the offspring of the parents is a mix of them ex: a red flower and a white flower = offspring is pink *the offspring is intermediate of both parents heterozygous phenotype= intermediate

Question 41

Codominance

Answer 41

not a mixture, but a heterozygote that exhibits both traits ex: if you have a pink parent and a white parent and the offspring is pink and white spotted

Question 42

ABO Blood System

Answer 42

type A blood is dominant to type O type B blood is dominant to type O ex: I^A and I^O = Type A blood AB blood type = I^A I^B

Question 43

X and Y chromosome genes

Answer 43

X chromosome = there are lot of genes on X chromosome Y chromosome = not as many genes - SRY gene is on Y chromosome (needed for male development) sex linked genes = genes on a sex chromosome X-linked genes = genes on the X chromosome - if you have one X and one Y, you're hemi (you only have one copy of each of those genes) *males are hemizygous for sex-linked genes (bc they only have one X and one Y chromosome)