1. THE HUMAN GENOME AND HEREDITY Nutrition and Gene Expression Jan 22, 2015

2. This graphic is a simple cartoon the genome (46 chromosomes). Most of your cells contain this complete set of chromosomes. (note FEMALE/MALE difference). If your progeny got exactly these genes, Then your progeny would be essentially your twin (except of course, much younger than you!). But that’s NOT what happens. Your children will have 46 chromosomes, but 23 of those chromosomes will be from the maternal set, and 23 of those will be from the paternal set.

3. 23 are selected for the ovum 23 are selected for the sperm The new embryo has a full set of 46 chromosomes MATERNAL SET PATERNAL SET

4. SIMPLE MITOSIS: Duplication of Chromosome 2. This happens as a regular part of each cell division, since each cell needs a complete copy of all the DNA in the cell. For a homework assignment, you will need to fill in the missing steps. SEVERAL STEPS

5. DNA REPLICATION: If every gene was copied perfectly, the genes in the gametes would be identical to the parental genes.

6. This is what is supposed to happen ATGCTAATGTGCCTAT ATACG TACGATTACACGGATATATGC ATGCTAATGTGCCTAT ATACG TACGATTACACGGATATATGC ATGCTAATGTGCCTAT ATACG TACGATTACACGGATATATGC TWO EXACT COPIES OF ORIGINAL DNA

7. BUT ONE COPY CAN HAVE THE WRONG DNA BASE! ATGCTAATGTGCCTAT ATACG TACGATTACACGGATATATGC ATGCTAATGTGCCTAT ATACG TACGATTACACGGATATATGC ATGCTAATGTGTCTAT ATACG TACGATTACACAGATATATGC DEFECTIVE COPY

8. A WHOLE REGION CAN BE DELETED ATGCTAATGTGCCTAT ATACG TACGATTACACGGATATATGC ATGCTAATGTGCCTAT ATACG TACGATTACACGGATATATGC ATGCTAATGTGCTATACG TACGATTACACGATATGC This copy has lost 3 bases from each strand

9. The duplication of the chromosomes during formation of gametes (eggs and sperm) is called MEIOSIS. This is different in fundamental ways from mitosis. The mechanism of meiosis explains major features of the way genes are passed on to the offspring. Mutations that occur here can be very significant as will be drawn on the board. MEIOSIS

10. THESE SLIDES HAVE COMPLEX NOTATION. FURTHER EXLANATION WILL BE PROVIDED DURING LECTURE. We use different codes, for example: #1 = chromosome 1 (forms a pair, in most cells) M = maternal chromosomes, P = paternal a,b = each of the two maternal chromosomes that can be provided to the gamete

11. DURING MEIOSIS, GAMETES ARE FORMED THAT ONLY HAVE ONE COPY OF EACH CHROMOSOME. THE EMBRYO OF COURSE HAS TWO COPIES. THE PROCESS IS VERY COMPLEX, AND IS OFTEN MISUNDERSTOOD. I WILL SHOW YOU GRAPHICALLY, IN THE FOLLOWING SLIDES, THE STEPS THAT ACTUALLY OCCUR IN THE FORMATION OF GAMETES. Ovum DNA Sperm DNA BOTH ARE HAPLOID DIPLOID EMBRYO Several steps

12. The following slides expand on the steps of meiosis. It is of interesting because it allows the MIXING of genetic material.

13. 1 CHROMOSOMES, SET 1 MEIOSIS: The process is shown only for the process in the ovum, it’s in the same in the sperm. We will illustrate this only for chromosome 1. When the DNA is duplicated for the ova, the female has a chromosome from her mother (a) and her father (b) that can be used. NOTICE THE COLOR DIFFERENCE BETWEEN MATERNA AND PATERNAL. abba ba STEP 1: Each copy of chromosome 1 is duplicated.

14. abba The chromosomes have been duplicated. Two of them MOVE within the cell, so the are directly adjacent. abba STEP 2: One of the copies from maternal, and one from paternal, pair up!

15. STEP 3 Part of the DNA sequence is exchanged between the two that are paired. (this is called: CROSSING OVER). abba RESULT: For 2 of the 4 chromosomes, there has been PARTIAL DNA exchange. This shows one exchange, there may be 2-3 crossovers ror each meiotic pair. ab/aba/b

16. a b b/a POSSIBLE DNA STRUCTURES FOR CHROMOSOME 1 IN THE OVUM From mother: no changes From father: no changes IN THIS DIAGRAM, MOTHER and FATHER REFER TO THE CHROMOSOME YOU GOT FROM EACH PARENT. NOTE: THE OVA AND SPERM ARE HAPLOID, AND HAVE ONLY 1 COPY OF EACH CHROMOSOME. Mixture/maternal and paternal Mixture/paternal and maternal

17. aba/bb/a WHEN THE OVA ARE FORMED, ONE COPY GOES TO EACH OVUM. a b a/b b/a

18. WHAT DOES THIS MEAN? It means that 50% of the time, the chromosome #1 that you provide your child has been REARRANGED so it has a mixture of your PATERNAL #1 DNA and your MATERNAL#1 DNA. You could also provide a chromosome #1 that is identical, to what you got from your father or from your mother.

19. The subject of genetic recombination is complicated, and often is misunderstood. We will revisit this topic for additional discussion in further lectures. THE NEXT TOPIC: Since you get 2 copies of most genes (one from each parent), what consequences can occur?