CHP 9; SEXUAL REPRODUCTION & MEIOSIS

reproduction

biological process by which new individual organisms (offspring) are produced from parents

asexual reproduction

when an organism copies its dna and splits the contents of one cell into two offspring that is identical (ex; binary fission)

sexual reproduction

requires combination of genetic material from two parents that results in the offspring looking different

genetic diversity

each of the resulting chromatids has a unique combination of alleles

ploidy

the number of set of chromosomes in a cell or organism

diploid cells

contain two full sets of chromosomes

karyotype

size ordered chart that are same for both sexes

autosomes

1-22 chromosomes that are the same for both sexes

sex chromosome

23th pair of chromosome which determines whether the individual is female or male

xx

female

xy

male

homologous pair

two chromosomes share the same size, centromere position, & pattern of light and dark staining bands

alleles

one of two or more alternative forms of a gene

unreplicated chromosome

typically carries exactly one allele of each genes, so a person inherits one allele per gene from each parent. (size= not in x form)

replicated chromosome

each chromosome consists of two identical sister chromatids (size= x form)

haploid cells

contain only one full set of genetic information

gametes

sperm and egg cells

fertilization

merges the gametes from two parents that creates a zygote

zygote

has two full sets of chromosomes and it begins dividing mitotically shortly after fertilization

mitotic cell division

produces the cells needed for growth, development, and tissue repair

meiosis

forms genetically variable nuclei, each containing half as many chromosomes as the organisms diploid cells, used in sexual reproduction and only occurs in testis & ovaries in humans

germ cells

can undergo both mitosis and meiosis

somatic cells

can only undergo mitosis and its the rest of the bodies diploid cells that doesn't participate directly in reproduction

mitotic cell cycle

includes 3 parts; interphase, mitosis, and cytokinesis. it creates identical copies by dna replication once and dividing once

interphase meiosis

cell grows, chromosomes and dna is replicated and it prepares for cell division

meiosis 1 and 2

distributes the dna from one specialized diploid cell into four haploid cell. also shuffles genetic information which sets the stage for each haploid nucleus to receive a unique mixture of alleles

meiosis 1

seperates homologous chromosomes into 2 haploid cells. includes early and late prophase, metaphase 1, anaphase 1, telophase 1, and cytokinesis

early prophase

chromosome condense and become visible

late prophase

crossing over, spindle forms and nuclear envelope breaks

metaphase 1

paired homologous chromosomes line up doubled filed along middle of the cell

metaphase plate

middle of the cell

anaphase 1

homologous chromosomes separate to opposite ends of the cell and sister chromatids remain together

telophase 1

nuclear envelope forms around chromosomes which may temporarily de condense and spindle fibers disappear

cytokinesis

divides the cell

meiosis 2

2 haploid cells divide into 4 haploid cells. includes prophase 2, metaphase 2, anaphase 2, telophase 2, and cytokinesis

interphase meiosis 2

chromosomes unfold into very thin threads, and the cell produces proteins but dna doesn’t replicate a 2nd time

prophase 2

spindles forms, nuclear envelope breaks

metaphase 2

chromosomes line up single filed along the middle of the cell

anaphase 2

centromeres split as sister chromatids separate to opposite ends of the cell

telophase 2

nuclear envelope assembles around daughter nuclei and chromosomes de condense and spindle fibers disappear

cytokinesis 2

divides cells, resulting in 4 non identical daughter cells each containing 2 chromosomes

human diploid cells

46 chromosomes

human gametes

are haploid containing 23 chromosomes

diploid zygote

when two haploid gametes combine in fertilization

crossing over

process in which two homologous chromosomes exchange genetic material which allows recombination of genes, results in 4 different genetic combinations after meiosis

recombinant chromatids

chromatid containing genetic information from both parents as a result of crossing over

parental chromatids

didn’t participate in crossing over, remain unchanged and genetic information is only from one parent

random orientation

many arrangements of homologous pairs of chromosomes are possible during metaphase 1 and each round of meiosis is most likely to produce daughter cells with different allele combinations

number of possible orientations

2, raised to the power of the number of chromosome pairs

monozygotic twins

identical because they come from the same zygote

dizygotic twins

fraternal because they start as two different zygotes, where two sperm cells fertilize two separate egg cells

monozygotic triplets

single embryo splits into 3 parts

trizygotic triplets

3 sperm may fertilize 3 separate egg cells

pair and spare

embryo splits and forms 2 identical babies, and a separate embryo into an additional, nonidentical baby

nondisjunction

when chromosomes or sister chromatids fail to separate at either anaphase 1 or anaphase 2

nondisjunction meiosis 1

homologous chromosomes fail to separate in anaphase 1, so one daughter cell receives one extra chromosome while the other receives none

nondisjunction meiosis 2

sister chromatids fail to separate in anaphase 2, resulting in the top 2 gametes to be normal while the bottom 2 gametes aren’t normal with one receiving one while the other doesn’t receive any

trisomy 21

when a person inherits 3 copies of chromosome 21 instead of 2, this occurs the most because the fetus is most likely to remain viable

trisonomies

most common include chromosomes 13, 18, and 21. few infants with trisomy 13 and 18 survive, most dying.

trisonomy 18

edwards syndrome

aneuploidy

unbalanced chromosome number, either more or less

lack x

when there’s no x chromosome, so much genetic material is missing that it probably cant sustain more than a few cell divisions

polyploid cell

cell with extra chromosome sets

total disjunction

occurs in stressful conditions, failure of the spindle to form properly during meiosis

xxy

klinefelter

xyy

jacobs syndrome

xo

turner syndrome