Section 3 - Genetics - Work of Mendel, genetic diagrams, sex-linked genetic disorders and inheritance of blood groups Flashcards
What had Mendel discovered and shown through his experiment with pea plants?
Height characteristic in pea plants was determined by separately inherited ‘hereditary units’ passed on from each parent. Ratio of offspring sizes showed unit for tall was dominant over dwarf.
What did Mendel do in one of his experiment with pea plants?
- crossed dwarf and tall pea plants with all 4 offspring produced were all tall
- bred two of these tall offspring. Found when offspring from first cross were crossed with each other, three tall offspring produced for every one dwarf overall. Ratio of 3:1 for tall:dwarf
What were the 3 important conclusions Mendel reached about heredity in plants?
- characteristics in plants determined by ‘heredity units’
- hereditary units are passed on to offspring unchanged from both parents, one unit from each parent
- hereditary units can be dominant or recessive
What are alleles?
Different versions of the same gene?
Difference between homozygous and heterozygous?
Homo - When an organism has two alleles for a particular gene that are the same
Hetero - When an organism has two alleles for a particular gene that are different
What is a phenotype?
The characteristic you have caused by your alleles
Which chromosomes do males and females have?
Male: XY
Female: XX
What is monohybrid inheritance?
The inheritance of a single characteristic
What does someone need to be a carrier of the gene?
They need just one copy of the allele
Two types of diagrams used to show monohybrid inheritance?
Monohybrid cross and Punnett square
Difference between Y and X chromosome?
Y is smaller than X and carries fewer genes. Y has one allele whilst X has two
How are men more likely than woman to show recessive characteristics fo genes that are sex-linked?
Men only have one X chromosome so often only have one allele for sex-linked genes, thus characteristic of this allele shown even if recessive
What are sex-linked genetic disorders?
Disorders caused by faulty alleles located on sex chromosomes
Which chromosome is responsible for colour blindness caused by a faulty allele?
X chromosome
How is colour blindness much rarer in women than in men?
Y chromosome doesn’t have allele for colour vision and women need two copies of recessive allele while men need one copy for disorder
