Chapter 16 2 Genetics Since Mendel Mr Perez

Chapter 16. 2 Genetics Since Mendel Mr. Perez

Important Vocabulary • Incomplete dominance • Polygenic inheritance • Sex-linked gene

Incomplete Dominance • After Mendel’s work was rediscovered in the 1900 s, scientists repeated his experiments. • Some plants produced results the same as Mendel, however, other plants produced different results

Incomplete Dominance • One scientist mixed purebred four-o’clock plants with purebred white four-o’clock plants • RESULTS: pink flowers • The pink flowers were then crossed with each other • RESULTS: red, pink and white flowers • Why do you think this happened?

Incomplete Dominance • This happened because… • When the red and white alleles combined, they formed an intermediate (in between) phenotype • Incomplete dominance: when the offspring of two homozygous parents produce intermediate phenotypes • Examples include: other flower colors and the color of a horse’s coat

Multiple Alleles • Mendel studied traits that were controlled by only two alleles, however, many traits are controlled by more than two alleles (multiple alleles) • Traits controlled by multiple alleles produce more than three phenotypes of that trait • Example: Blood type

Multiple Alleles • Blood types

Incomplete Dominance Practice • Write the following punnett squares and answers on your punnett square practice worksheet. http: //sciencespot. net/Media/gen_spbobincdom. pdf

Polygenic Inheritance • Polygenic inheritance: occurs when a group of gene pairs work together to produce a trait • Examples: eye color, height, skin and hair color • The environment plays a large role in the expression of traits in polygenic inheritance • The effects of many alleles produces a wide variety of phenotypes • Which is why it’s so hard to classify the different shades of eye color!

Impact of the Environment • The environment plays a role in how some genes are expressed or whether they are expressed at all • Although genes determine many of your traits, you might be able to influence their expression by the decisions you make • For instance, if some people at risk for skin cancer limit their exposure to the Sun and take care of their skin, they might never develop cancer.

Impact of the Environment

Human Genes and Mutations • Remember, mutations are permanent changes in genes • They occur when: 1. DNA is copied incorrectly 2. Mutagens (X-ray, chemical, sun exposure) damage DNA 3. Added or subtracted chromosomes • Not all mutations are bad!

Recessive Genetic Disorders • Many human genetic disorders are caused by recessive genes, carried by both parents • These parents are called carriers • They do not show the disorder because they are heterozygous • Examples: cystic fibrosis

Cystic Fibrosis

Sex Determination • In humans… • Female eggs contain an X chromosome • Male sperm may contain an X or a Y chromosome • Females are XX • Males are XY

Sex-Linked Disorders • Sex-linked gene: allele found on a sex chromosome • Sex-linked disorders are conditions that result from inheriting a sex-linked gene • Example: Red-green color-blindness • Found on X chromosome • Recessive sex-linked disorder • In females with two X chromosomes with recessive allele • In males with only one X chromosome with recessive allele

Pedigrees Trace Traits • Pedigree: visual tool used for following a trait through generations of a family

Using Pedigrees • Squares represent males • Circle represent females • A completely filled in square or circle shows that trait is shown • Half colored circles or squares show carriers (heterozygous) • Empty circles or squares do not show the trait and are not carriers

Links • http: //highered. mcgrawhill. com/sites/0072485949/student_view 0/chapter 3/interactive_activity. html • http: //www. zerobio. com/drag_gr 11/pedigree/pedig ree 1. htm

Resources • Florida Science Grade 8 • Glencoe Science & Mc. Graw Hill Publishing • Google Images