Human Heredity Chapter 14-1 Biology Mr. Hines

Decades ago, biology was limited to the study of living things other than humans. We knew more about pea plants and fruit flies than humans. Why? It is unethical to perform experiments on humans. Today, we can do this without harming humans. So today, we know a lot about humans. This section will deal with mostly human heredity

What is a karyotype? During mitosis, the chromosomes inside of the nucleus become visible. Scientists can take a photograph of the chromosomes. The photograph is then enlarged and used to identify the chromosomes in humans. Humans have 23 pair of chromosomes – one set from mom and one from dad. Therefore, humans have a total of 46 chromosomes.

Furthermore, the chromosomes can be identified and labeled – numbers 1-23. The chromosomes are then grouped and placed in the proper order. Typically, they are in order from largest to smallest. Chromosomes 23 are called sex chromosomes – Usually labeled X and Y

What is a karyotype? A Karyotype is chart of the chromosomes displayed in the proper order. A karyotype is made from a photograph of the chromosomes within the nucleus.

Here is a real karyotype

22 of the 23 human chromosomes are called “autosomes.” Again, the 23rd chromosomes are called “sex chromosomes. So humans have 22 pair of autosomes and 1 pair of sex chromosomes. Total chromosomes = 46

So, what are sex chromosomes Sex chromosomes are what determines our sex. Males and Females have certain traits – determined by the genes located on the 23rd chromosomes. List some traits of males and females *males list female traits, *females list male traits

Punnett square for sex determination Female chromosome = X Male chromosome = Y Which is dominant? You decide?

If dad is a male and mom is a female Then how do offspring inherit sex? Remember, this is called segregation of alleles. X and Y chromosomes will segregate into separate sex cells.

Male XY x Female XX Cross XY and XX

What is the probability of having a boy or a girl? Why? Be able to answer that question on a test.

Pedigrees A pedigree is a chart that helps us better understand the genetics in a particular family. A pedigree also shows the relationships within a family.

Color blindness and sex linked genes Color blindness is a trait that some people have where they can not see certain colors. There are 2 alleles for color vision C = normal vision c = color blind Normal vision is Dominant

It is written like this XC = normal vision Xc = color blind Y = the Y chromosome never carries the gene. So we say that color blindness is sex linked – meaning that it can only be carried by the female X chromosome.

Consider this cross Mom XCXc *mom has normal vision because she carries the dominant C gene *mom is a carrier of the gene Dad XCY *dad has normal vision because he has only the dominant C gene

Punnett square

Color blindness

Lets say mom and dad have 4 children with the following outcome Write the genotype next to each person

Perform a cross for this mother and father

Perform a cross with this mother and father

Create crossing that results in a colorblind female