Meiosis 1 Write the date 2 Write the

Meiosis 1. Write the date 2. Write the title 3. Starter: a) Name 2 sources of variation in meiosis. b) Where does meiosis happen in a human? In a plant? c) What is an allele? 26 December 2021 Today I am learning üthat a locus (loci) is the location of genes on a chromosome üthe linkage of genes on a chromosome and sex linkage.

Functions of Meiosis I and Meiosis II • Meiosis I generates genetic variation due to crossing over and independent assortment and separates homologous chromosomes into cells • Meiosis II separates sister chromatids into daughter cells

Loci and Sex Linkage

Gene Locus • A locus (plural loci): the position on a chromosome. • A variant of the similar DNA sequence located at a given locus is called an allele.

http: //study. com/academy/lesson/geneticlinkage-definition-analysis. html *http: //study. com/academy/lesson/linkedgenes-definition-examples-quiz. html

Linkage • Some characteristics tend to be inherited together. • Genes are inherited independently only if they are on separate chromosomes or far apart on same chromosome. • Any 2 genes with a locus on the same chromosome: linked together and passed as a pair to the same gamete.

Linkage

Linkage • Crossing the heterozygous individuals does not produce the full range of characteristics expected if the genes were inherited independently. 3: 1 ratio is typical of monohybrid inheritance.

Sex Linkage -occurs when the genes for a certain characteristic are carried on the sex chromosomes. **They do not determine the sex of the organism, they just happen to occur on the sex chromosomes. Fyi: The Y chromosome is shorter than the X chromosome, so it carries fewer alleles.

Colour blindness The allele for colour vision is carried on the part of the X chromosome that is missing from the Y chromosome. Colour blindness caused by recessive allele. Females inherit 2 alleles for colour vision, one on each X chromosome, if they inherit one faulty allele, they are unaffected. Males only inherit one allele from their mother, if they inherit the faulty allele they are colour blind. As a result, colour blindness is more prevalent in males.

Haemophilia is another example of sex linked inheritance, where females can be unaffected carriers, but males will suffer from the disease if they inherit the faulty allele. Normal Carrier Gametes XH Xh XH XH Xh Y XH Y Xh Y Normal Sufferer

X Chromosome Inactivation Early in a female’s embryonic development, one of the X chromosomes is inactivated. This occurs randomly in each cell: have either their maternal or paternal X chromosome switched off. Tortoiseshell cats will have a unique pattern depending upon which chromosome is switched off, as one carries the black gene and one carries the orange gene.

Questions 1. If the genes in peas for tall and purple flowers were linked and always inherited together, and so were the short and white flowers genes, what would be the outcome of mating two tall purple flowers? 2. Explain how it is possible for a colour blind girl to occur. 3. A couple had children using IVF because the father has haemophilia, a sex-linked condition. Only female embryos were used. Explain whether or not future generations of this family would be free of haemophilia.

Answers 1. 75% tall purple and 25% short white 2. When a colour blind man has children with a heterozygous woman. The allele for colour blindness can then be passed to a daughter in the X chromosome for each parent. 3. The family would not be free of haemophilia because their daughters would be carriers. Half the sons of the carrier daughters would be expected to have the condition.

Questions 1. The genotype and phenotype of certain cat colours are shown in the table: Phenotype Genotype Male Female Black Xg Y Xg Xg Ginger XG Y XG XG Tortoiseshell - XG Xg A breeder has a number of black, ginger, and tortoiseshell cats. a) If she wants all the female kittens to be tortoiseshell, what are the genotypes and phenotypes of the parents she should use? b) What will be the phenotypes of the male kittens in the crosses you have suggested?

Task: Complete the Unit 2 practice past paper. It will be peer corrected. You will receive a mark out of 30.