Sexual Reproduction Enhances Genetic Diversity

Vocabulary Gene, Allele Homozygous, heterozygous Trait Genotype Phenotype Dominance Punnett square

Sexual Reproduction Enhances Genetic Diversity Genetic diversity is the variation of the genetic information among individuals of a population

Three main sources of genetic variability Independent Assortment Crossing over Random Fertilization

Independent Assortment Independent assortment is the random alignment of homologous chromosomes during meiosis I and of non- identical sister chromatids during meiosis II.

Three Sources of Genetic Variability Crossing over between homologous chromosomes during prophase I,  chromosomes with new combinations of genes.

Three Sources of Genetic Variability Random fertilization of an ovum by a sperm: Any sperm can fuse with any ovum About 64 trillion diploid combinations Each zygote has a unique identity

Alleles We have two sets of chromosomes (one from mom, one from dad). Genes are on our chromosomes. Therefore we have two sets of genes (one from mom, one from dad). The different form of each gene is called an allele.

Genotype Our genotype is the specific allelic combination an individual has. Alleles can be represented with a letter Eg. Allele for black fur may be represented by B

Dominance One allele may be dominant over the other and therefore it’s trait will be expressed. Eg. Black fur may be dominant over white fur Dominant alleles are assigned a capital letter (B) Recessive alleles are in lower case (b).

Dominance If a cat has both alleles for black fur its genotype would be BB and it will have black fur. If a cat has Bb, (one for black, one for white) as black allele is dominant, it’s trait will be expressed and the cat will have black fur. A recessive allele will only be expressed if both chromosomes contain the recessive allele. bb

Dominance Eg. The allele for Widows Peak is dominant, while the allele for a straight hairline is recessive.

Dominance If an individual has one or both chromosomes containing alleles for widow’s peak, that trait will be expressed. A person will only display a straight hairline if both chromosomes contain the recessive allele.

Phenotype Phenotype is the visible trait that is expressed The allele for Widow’s Peak could be “W” The allele for straight hairline (recessive) = “w” Phenotype is determined by the genotype: Genotype = Ww  Phenotype = widow’s peak Genotype = ww  Phenotype = straight hairline

What are the phenotypes for the following genotypes regarding fur colour? (B = black, b = white) BB Bb bb

Genotypes Homozygous – having two of the same alleles for the same gene ( eg. BB or bb, WW or ww). Heterozygous – having two different alleles for the same gene (eg. Bb, or Ww).

Why is Genetic Diversity Important? Genetic diversity serves as a way for populations to adapt to changing environments and therefore survive to reproduce, ensuring the continuation of the species. Outbreaks of disease kills large numbers of population but there is always a few who were able to fight it. They survived and reproduced, passing on their ability to fight the disease to their children, strengthening the population.

Advantages and Disadvantages of Sexual Reproduction Genetic Diversity An individual needs to find a mate. Fewer offspring produced Slower Most individuals have to grow and develop for 8-10 years before mature enough to reproduce.

Advantages and Disadvantages of Asexual Reproduction If parent does well, so do offspring because they are genetically identical to parent. Only one parent necessary - less time and energy spent attracting a mate Parent can reproduce frequently and reproduce many offspring in relatively short period of time. No genetic diversity – entire populate susceptible to disease or negative change in habitat.

Activity: Traits Lab Homework: Read pages 79-81 Answer CYU p82 #1-6, 9-13 Complete Traits lab

CHAPTER Sexual Reproduction 3 With a partner, draw a comparison table like the one below on a sheet of paper. In the table, list some advantages and disadvantages of sexual and asexual reproduction. Read pages 80 and 81 in your textbook. Compare the advantages and disadvantages suggested in the reading with those you and your partner described in your table. Complete your table with any points you may have missed. Advantages Disadvantages Sexual Reproduction Asexual Reproduction