Your Vocabulary words-- write into your journal:

Transcription

1 HUMAN INHERITANCE

2 Your Vocabulary words-- write into your journal: 1. Multiple alleles: three or more forms of a gene that code for a single trait. 2. Sex chromosomes: these carry genes that determine whether a person is male or female. They also carry genes that determine other traits. 3. Sex-linked gene: because the alleles are passed from parent to child on a sex chromosome those traits controlled by a sex-linked gene are called sex-linked traits. 4. Carrier: is a person who has one recessive allele for a trait and one dominant allele. A carrier of a trait controlled by a recessive allele does not have the trait but can pass it on to his/her offspring. (Color blindness is a good example of this).

3 Why Children resemble their Parents--- Because they INHERIT their genes from them:

4 When babies are born.... Everyone always tries to decide who the baby looks like. Often the baby resembles mom and dad or just more like one or the other and even perhaps an uncle or aunt is who the baby may look like. Why? Because all the genes get passed and jumbled and passed and jumbled, etc.

5 Look around your classroom... Some students have curly hair Some students have straight hair Some students are tall Some students are short Get the picture all different

6 Remember that what you see is the phenotype and what you cannot see is the genotype Phenotype is like a photograph!!! I see this.... One can roll the tongue and one cannot. What I cannot see is their genotype.. The one who cannot roll their tongue has two recessive rr genes.

7 OK---back to where we were---everyone in your class is different due to their genes. And those genes came from who? Right! Their biological parents Some of our inherited traits come from a single gene. Some traits come from multiple alleles of a gene. That just means that several genes act together to form the trait. Examples of multiple alleles would be skin and eye color.

8 Examples of single gene would be: One mentioned in your book is the widow s peak hairline. It is a dominant trait. If a person has that dominant gene, they would have a widow s peak. Someone with 2 recessives genes would have a straight hairline.

9 Another example of multiple gene influence is blood type:

10 So.. When the trait is influenced by a single gene, that one gene determines the outcome or the look. When it is multiple genes they act together to produce one trait this may seem odd since genes are in pairs and so only two really influence that outcome of the look. So what about codominant alleles then? Both act as a dominant and BOTH traits will show. It is known that at least 4 genes control height so if they act together to come up with one trait, you can understand why there are so many different sizes of people with their height.

11 Sex Chromosomes!! Do we have to talk about this!!!!!!

12 It is very simple, really Males have a X and a Y chromosome. Females have two X chromosomes.. So the sex chromosomes are the only ones that do NOT match.

13 So, what happens? When the egg and sperm cells form, females sex chromosomes are both X. So, if you are a girl, your two sex chromosomes match. If you are a male, your sex chromosomes do not match. One is an X and one is a Y chromosome. The Y chromosome is much smaller than the X.

14 So let s look at how you became a male or female, shall we? Since both of a female s sex chromosomes are X chromosomes, all eggs carry one X chromosome. Males, however, have two different sex chromosomes. Therefore, half of a male s sperm cells carry an X chromosome, while half carry a Y chromosome. When a sperm cell with an X chromosome fertilizes an egg, the egg has two X chromosomes. That fertilized egg will develop into a girl When a sperm with a Y chromosome fertilizes an egg, the egg has one X chromosome and one Y chromosome so the fertilized egg will develop into a boy.

15 Now, sex linked diseases should make complete sense to you: Some genes for human traits are carried on the sex chromosomes. Those genes are called sex-linked genes because their alleles are passed from parent to child on a sex chromosome. That makes those traits controlled by sex-linked genes called sex-linked traits. One example is red-green colorblindness. A person with this trait cannot distinguish between the colors red and green. Females have two X chromosomes, whereas males have one X and one Y chromosome. Most of the genes on the X chromosome are not on the Y chromosome. Therefore, an allele on an X chromosome may not have a corresponding allele on the Y chromosome. Sex-linked genes can have dominant and recessive alleles, just like other genes. So

16 How do these genes get passed along? 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 a recessive allele on the other 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. Therefore, because males have only one X chromosome, males are more likely than females to have a sex-linked trait that is controlled by a recessive gene. Huh! That makes sense to me now!!

17 Exactly how does this colorblindness come about then? It is a trait controlled by a recessive allele on the X chromosome. Many more males than females have red-green colorblindness. You can understand why by looking at the Punnett square. One parent is normal and one has colorblind vision. But, the mother is a carrier of color blindness. A carrier is a person who does not show the trait or is not colorblind but can pass that gene on to an offspring. It is recessive so with a male, there are not two X chromosomes---one to hide the recessive, so the gene for colorblindness is then manifested (shows up). Notice none of the girls are color blind, but one is a carrier. Males need only inherit one of the X chromosomes to be colorblind as there is only one X already there, so the recessive will show up.

18 What about the effect/s of our environment? Our environment CAN affect our genes. The environment is our surroundings. A person s height is controlled by multiple alleles. But, the height may also be influenced by the environment. HOW? The food you eat in your environment can affect how you grow. A diet lacking in protein, certain minerals, or vitamins can prevent a person from growing as tall as they might have if the food eaten had been complete. Another example that can be affected are skills such as playing a musical instrument. Your muscle coordination and hearing correct notes will help you play well. You would also need instruction. This would allow you to not inherit the skill but through practice and instruction you would acquire the musical skill. You may inherit the long fingers to play the piano but unless there is some instruction and practice, you will not be very good.

19 Did we cover it all? What are some patterns of inheritance in humans? Hair curly or straight; eyes many colors, height many sizes; skin color many. What are the functions of the sex chromosomes? To determine if you are a male or female. What is the relationship between genes and the environment? Environment can influence your inherited genes for better or worse.

20 OK we are good!!