Chapter 5:1 Human Inheritance

Different traits are determined by a variety of inheritance patterns Single Genes with two alleles Single Genes with two alleles Single genes with multiple alleles Single genes with multiple alleles Many genes that act together Many genes that act together

Patterns of Human Inheritance We’ve studied traits controlled by one single gene with dominant and recessive alleles. We’ve studied traits controlled by one single gene with dominant and recessive alleles. ex: widow’s peak ex: widow’s peak

? For you… The probability that two heterozygous parents for widow’s peak will have a child with a straight hairline is _____ percent. The probability that two heterozygous parents for widow’s peak will have a child with a straight hairline is _____ percent.

Answer for you 25%

A gene with three or more alleles for a single trait has _multiple alleles____ A gene with three or more alleles for a single trait has _multiple alleles____ Human blood type has more than two alleles. How many can you count? Human blood type has more than two alleles. How many can you count? Single Genes with multiple alleles

? For you… Is the following sentence true or false? Even though a gene has multiple alleles, a person can carry only two of those alleles. Is the following sentence true or false? Even though a gene has multiple alleles, a person can carry only two of those alleles.

Answer for you true FYI – the gene for tabby stripes in cats has multiple alleles

Traits Controlled by Many Genes When a large number a are possible, usually the trait is controlled by many genes. When a large number a phenotypes are possible, usually the trait is controlled by many genes.

Traits controlled by Many Genes Traits such as height and Traits such as height and skin color are examples. are examples.

The Sex Chromosomes. Determine weather a person is male or female.

Sex Chromosomes They can carry genes that determine other traits as well They can carry genes that determine other traits as well They are one of the They are one of the 23 pairs of chromosomes. 23 pairs of chromosomes.

Girl or Boy XX is a girl XY is a boy

Sex Chromosomes and Fertilization What happens to the sex chromosomes when egg and sperm cells form? What happens to the sex chromosomes when egg and sperm cells form? All eggs carry one X chromosome. Why? All eggs carry one X chromosome. Why? Half of a male’s sperm cells carry an X chromosome, while half carry a Y chromosome. Half of a male’s sperm cells carry an X chromosome, while half carry a Y chromosome.

Sex Chromosomes and Fertilization Who determines the sex of a baby the man or the woman? Duh…the man. Was it King Henry VIII who killed wives for not giving him a son? Not too bright!!!

Race to Ellen Egg

? For you… 4. Circle the letter of each sentence that is true about human sex chromosomes. a. All eggs carry one X chromosome. b. Half of a male’s sperm cells have an X chromosome. c. None of a male’s sperm cells have a Y chromosome. d. The egg determines the sex of the child

Answer for you 4. Circle the letter of each sentence that is true about human sex chromosomes. a. All eggs carry one X chromosome. b. Half of a male’s sperm cells have an X chromosome. c. None of a male’s sperm cells have a Y chromosome. d. The egg determines the sex of the child

Sex-Linked Genes Genes on the X or the Y chromosome are sex linked genes. Genes on the X or the Y chromosome are sex linked genes. An example of this is red-green colorblindness An example of this is red-green colorblindness Let’s read about this…p. 149 Let’s read about this…p. 149

Like other genes, sex-linked genes can have dominant and recessive alleles. Like other genes, sex-linked genes can have dominant and recessive alleles. In females, a dominant allele on one X chromosome will mask a recessive allele on the other X chromosome. But in males, there is usually no matching allele on the Y chromosome to mask the allele on the X chromosome. In females, a dominant allele on one X chromosome will mask a recessive allele on the other X chromosome. But in males, there is usually no matching allele on the Y chromosome to mask the allele on the X chromosome. As a result, any allele on the X chromosome—even a recessive allele—will produce the trait in a male who inherits it. As a result, any allele on the X chromosome—even a recessive allele—will produce the trait in a male who inherits it.

Punnett square for color blindness

? For you… An example of a sex linked trait controlled by a recessive allele is color blindness. This is more common in men than in women. Why? An example of a sex linked trait controlled by a recessive allele is color blindness. This is more common in men than in women. Why?

Because males have only one X chromosome -- they are XY. Since color blindness is carried on the X, even though it’s recessive, males don’t have anything to mask it. Because males have only one X chromosome -- they are XY. Since color blindness is carried on the X, even though it’s recessive, males don’t have anything to mask it. X c Y Answer for you…

Red Green Colorblindness A girl who receives only one recessive allele (written X c ) for red-green colorblindness will not have the trait. However, a boy who receives one recessive allele will be colorblind. A girl who receives only one recessive allele (written X c ) for red-green colorblindness will not have the trait. However, a boy who receives one recessive allele will be colorblind.

Carrier – a person who has one recessive allele for a trait and one dominant allele. Carrier – a person who has one recessive allele for a trait and one dominant allele. ? For you… true or false? A carrier for colorblindness is colorblind. ? For you… true or false? A carrier for colorblindness is colorblind.

Answer for you False!!!

? For you… What is the sex of a person who is a carrier for colorblindness? What is the sex of a person who is a carrier for colorblindness?

Answer for you… The sex of a person who is a carrier here is:Female

Another ? for you… Why is a son who receives the allele for colorblindness from his mother always colorblind? Why is a son who receives the allele for colorblindness from his mother always colorblind?

Answer for you… Why is a son who receives the allele for colorblindness from his mother always colorblind? Why is a son who receives the allele for colorblindness from his mother always colorblind? There is no allele on the Y chromosome that could mask the recessive allele for colorblindness on the X chromosome

One more ? For you… What allele combination would a daughter need to inherit to be colorblind? What allele combination would a daughter need to inherit to be colorblind?

Answer for you For a woman to be color blind she would have to have the genotype: X C

The Effect of Environment A. The effects of genes are often altered by the __environment______. A. The effects of genes are often altered by the __environment______.

Environmental Factors An example of an environmental factor that can affect a person’s height: An example of an environmental factor that can affect a person’s height: a person’s diet

Mini video on color blindness