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Chapter 10

Linked genes are genes located on the same chromosome. A dihybrid cross involves tracking two gene pairs through meiosis and determining the potential offspring genotypes using a Punnett square. Mendel's law of independent assortment states that alleles of different genes assort independently of each other during gamete formation because the genes are located on different chromosomes. A cross between two linked genes on the same chromosome will not produce a 9:3:3:1 ratio due to their close proximity preventing independent assortment, and recombination during meiosis can cause new allele combinations.

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Chapter 10

Linked genes are genes located on the same chromosome. A dihybrid cross involves tracking two gene pairs through meiosis and determining the potential offspring genotypes using a Punnett square. Mendel's law of independent assortment states that alleles of different genes assort independently of each other during gamete formation because the genes are located on different chromosomes. A cross between two linked genes on the same chromosome will not produce a 9:3:3:1 ratio due to their close proximity preventing independent assortment, and recombination during meiosis can cause new allele combinations.

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Term Definition

Linked genes Genes on the same chromosome

Steps to complete a dihybrid cross


- Step 1: Designate characters to represent the alleles
- Step 2: Write down the genotype and phenotype of the parents generation e.g. Rr Yy
- Step 3: Write down all potential gamete combinations for both parents (FOIL)
- Step 4: Use a punt square to work out potential genotypes of offspring
- Step 5: Write out the phenotype ratios of potential offspring

Outline the relationship between Mendel’s law of independent assortment


and meiosis
- Law of segregation states that for a pair of alleles, each gamete receives only one of the alleles
- Meiosis has two divisions
- Cells go from diploid to haploid
- Law of independent assortment states that the segregation of alleles of one gene is independent
of the segregation of the alleles of another gene
- Alleles are inherited independently
- Genes are on different chromosomes
- Presence of one allele does not influence presence of other allele
- Dihybrid crosses
- All allele combinations
- Ratio of 9:3:3:1
- 9:3:3:1 shows equal probability of all gametes
- Orientation of homologous chromosomes is random
- Orientation of one bivalent does not affect orientation of other in metaphase I

Explain a cross between two linked genes


- Linked genes occur on the same chromatid
- Genes inherited together do not segregate independently
- non 9:3:3:1
- Key for alleles involved in the example of a cross
- Homozygous parental genotypes and phenotypes shown
- F1 genotype and phenotype shown
- Possible F2 genotype shown
- Recombinants identified

- Recombinants due to crossing over


- In prophase I of meiosis
- Explanation of mutual exchange of parts of chromatids during crossing over

Chi-square
- Used to compare observed and expected values
- Chi-square value is obtained. Statistical table is used to determine probability 


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