Inheritance Flashcards
why does meiosis take place?
create unique gametes + ensures all organisms have the correct number of chromosomes
how many cells produced from meiosis?
4 genetically different daughter cells
what happens during anaphase 2?
chromosomes are pulled to opposite poles, forming 4 groups of chromosomes that have 1/2 the number of original diploid
what is independent assortment?
the production of different combinations of alleles in dauvghter cells, as a result of the random alignment of bivalents on the equator of the spingle in metaphse I of meiosis.
what is polyploidy
What is autosomal linkage?
the prescene of 2 genes on the same autosome so that they tend to be inherited together and do not assort independently
Mendels law of segregation
What is epistasis?
it is when one gene may effect the expression of another gene at a different loci
e.g. allele G = coloured feathers allele g = no colour, but even if have allele G, if there is allele F there is no coloured feather. the presence of allele F controls the expression of allele G
what is the chiasma?
position on a chromatid where crossing over of non-sister chromatids of homologous chromosomes occurs
what is a gamete?
a sex cell: sperm and egg
Define haploid and diploid.
diploid = 2 complete sets of chromosomes, 2n
haploid = 1 complete set of chromosomes, n
What is a zygote?
a cell formed at fertilisation, at the fusion of the nuclei of 2 gametes, diploid 2n
What are homologous chromosomes?
two chromosomes that carry the same genes in the same positions/loci
What is fertilisation?
the fusing of the nuclei of 2 gametes, to form a zygote
What is a gene?
a section of DNA on a chromosome which codes for a specific protein or polypeptide.
What happens in prophase I?
5 things
chromosomes condense and become visible; arrange in homologous pairs = forms bivalents; can have crossing over occurring, w/ chiasma ; centrioles migrate to opposite ends of the call to form spindle fibres made from microtubules; nuclear envelope breaks down; nucleolus disappears
What happens in metaphase I?
spindle fibres attach to the centromeres of the homologues pairs of chromosomes
What does the chiasmata do?
the 2 homologous chromosomes together in the bivalent are attached to each other through the chiasma. helps hold the homologous chromosomes in the bivalent in meiosis.
What is crossing over?
the exchange of alleles between non-sister chromatids of homologous chromosomes (part of a chromatid on one homologous chromosome is broken and rejoined on another chromatid from the other homologous chromosome)
What happens in anaphase I?
bivalent pulled apart, 1 chromosome to each pole; centromeres remain in tact holding 2 chromatids from each chromosome together; pulled by microtubules
What happens in telophase I?
spindle fibres break down; nuclear envelope forms around each set of homologous chromosomes; nucleolus reforms
What happens in meosis I?
a reduction division -> went from diploid to haploid
What is a reduction division?
nuclear division that results in the reduction in chromosome number
What follows telophase I?
cytokinesis, forms 2 cells
How does meiosis cause genetic variation?
- random assortment
- crossing over
- random fertilisation
What happens in prophase II?
centrioles migrate to opposite ends of the call to form spindle fibres made from microtubules; nuclear envelope breaks down; nucleolus disappears
What happens in metaphase II?
chromosomes line up along the equator; spindle fibres attached to centromeres
What happens in anaphase II?
centromeres divide; chromatids pulled to opposite poles by microtubules
What is the final result of telophase II?
4 genetically different daughter cells
How does crossing over create genetic variation?
by producing random different combinations of alleles on each chromatid. so the 4 daughter cells recieive one chromatid each, and the alleles on them will be different to original. 4 different gametes.
How does independent assortment result in genetic variation?
the bivalents will align randomly along the equator in metaphse I. their orientation is completely random and the orientation of 1 bivalent will not influence another. So the mix of alleles that each gamete recieves is random and different.
genotype vs. phenotype?
genotype = the alleles possessed
phenotype = the feature observed
what are codominant alleles?
when both codomiant alleles are present in the genotype, they are both also in the phenotype - they are both expressed
How do you do a test cross?
test with homozygous recessive to determine if organism is homozygous or heterozygous
what is a sex linked gene?
a gene found on a sex chromosome that is not found on the other sex chromosome
what is a carrier?
individual who possessed a particular allele in its geneotype, but it is not present in its phenotype (it is not expressed) due to being masked by a dominant allele, but the allele can be passed down to its offspring
- a heterozygote for a recessive characteristic
What increases the chances of autosomal linkage?
if the 2 genes are very close to one another on the chromatid otherwise could be separated during crossing over in prophase I
