Topic 3- gametes Flashcards
ovum
contains zona pellucida
contains haploid nucleus
cortical granules release substances causing ZP to harden
follicle cells form protective coating around egg
spermatozoa
sperm cells contain many mitochondria to provide energy for rotation of flagellum
acrosomes
in spermatozoa
contain digestive enzymes to break down ZP
allow sperm to penetrate egg
fertilisation
sperm head meets ZP
acrosome reaction occurs
sperm head fuses with cell membrane of egg
sperm nucleus enters egg
cortical reaction occurs (ZP hardens)
nuclei fuse
full set of chromosomes restored
diploid zygote formed
locus
location of gene on chromosome
closer the loci on chromosome the more closely linked they are
less likely to be separated during recombination in meiosis
autosomally linked
term describing alleles on same chromosome inherited as if they were the same gene (more or less)
sex linked genes
occur on X chromosome
y is smaller than x
cell cycle
cells divide to produce two genetically identical daughter cells
for growth, repair and asexual reproduction
stages of cell cycle
mitosis- PMAT
cytokinesis- cytoplasm devides
Interphase- G1,S,G2
meiosis
form of cell division
gives rise to genetic variation
produces haploid gametes
maintains chromosome number
crossing over
allows genetic variation
exchange of sections of DNA between homologous chromosomes
independent assortment
genetic variation
combinations of ways maternal/paternal chromosomes can be distributed between two daughter cells
chromosome mutations
translocation- swapping of genes, can be balanced or unbalanced
duplication
deletion
inversion
aneuploidy
changes to number of chromosomes
result of non-disjunction
homologous chromosomes/ sister chromatids fail to separate
polysomy
more than two chromosomes in a pair
down’s syndrome- trisomy-21
