Inheritance, Variation and Evoloution Flashcards
Meiosis
A special type of cell division producing gametes
Happens in sex organs
Ovaries and testes
Gametes contain half the number of chromosomes 23. This is called haploid.
Normal body cells contain 46 chromosomes. This is called diploid.
Meiosis results in variation
Diploid cells have pairs of chromosomes- Why?
One maternal and one paternal
In this pair the chromosomes are said to be homologous
what does sexual reproduction involve
fusion of male and female gametes, bc there are 2 parents the offspring contain a mixture of their parents genes
the mixture of genetic information produces what?
variation
what happens in asexual reproduction?
only one parent
no fusion of gametes
no mixing of chromosomes
no genetic variation between parent and offspring
the offspring are genetically identical to the parent
clones
what are the stages of meosis?
1) genetic information duplicates forming 2 armed chromosomes - one arm of each chromosome is an exact copy of the other arm. after replication the chromosomes arrange themselves into pairs
2) in the first division the chromosome pairs line up at the centre of the cell
3) pairs pulled apart so each new cell has one copy of each chromosome. some of mothers and fathers chromosomes go into each new cell
4) in the second division, the chromosome line up again at the centre of the cell. the arms of the chromosomes are pulled apart
5) four gametes are made each with only a single set of chromosomes in it. each gamete is genetically different from the others because the chromosomes all get shuffled up during meiosis each gamete only gets half of them, at random
what happens in mitosis that makes up a whole organism?
after 2 gametes have fused during fertilisation, mitosis , means the new cell divided to make a copy of itself, this keeps happening to produce lots of cells in an embryo. as the embryo develops these cells then start to differentiate into different types of specialised cells that make up an entire organism
what happens in sexual reproduction?
male and female gametes fuse. offspring have two parents so the offspring genes are a mix of mum and dads genes
how many chromosomes are in every human cell?
23 pairs
22 are matched pair of chromosomes that control…..
characteristics
the 23 pair are labelled…..
XX or XY
what do the XX and XY chromosomes decide?
your sex
males have ………. chromosme
XY
females have an ,,,,,,,,,,,,,,,,,,,,,,,,,,, chromsome
XX
punnet square for a boy
50 % chance
what genes you inherit contol what ………………..
characteristics you develop
what is a homozygous gene
when an organism has 2 alleles for a particular gene that are the same
what is a heterozygous
when 2 alleles for a particular gene are different
what is the dominant allele
When displayed the characteristic is always shown
Can be heterozygous or homozygous
E.g BB or Bb
Recessive alleles:
Only shown when the alleles are the same (homozygous)
E.g bb - blue eyes
phenotype
normal
what is cystic fibrosis caused by
a recessive allele
what is polydactyly caused by
a dominal allele
GENOTYPE
The alleles the person has