1. GENES AND HEREDITY

2. Students will recognize how biological traits are passed on to successive generations.

3. The Inheritance of Traits
Most children are similar to their parents
Children tend to be similar to siblings
Each child is a combination of parental traits
The combination of paternal traits and maternal traits is unique for each individual child

4. The Human Life Cycle
gametes (a male sperm cell + a female egg cell) fuse during fertilization to form a single celled zygote, or embryo
the embryo grows by cell division in mitosis
the embryo grows into a child
the child matures into an adult

5. Figure 6.1 The human life cycle.
A human baby forms from the fusion of an egg cell from its mother and a sperm cell from its father. The single cell that results from this fusion will grow and divide into trillions of cells, each carrying the same information.

6. Deoxyribonucleic Acid
All living things contain:
Deoxyribonucleic Acid
DNA
Control the structure and function of cells
When organisms reproduce, they pass on copies of their DNA to their offspring.
Because offspring have DNA from their parents, they will resemble their parents.

7. DNA is sort of like an instruction manual that shows how to build and maintain a living organism…

8. Genes
segments of DNA that carry information about how to make proteins
Structural proteins – for things like hair
Functional proteins – for things like breaking down lactose

9. Genes Are on Chromosomes
located on the chromosomes
number of chromosomes depends on the organism
Bacteria – one circular chromosome
Humans – 23 homologous pairs of linear chromosomes; one came from mom and the other from dad

10. Figure 6.3 The formation of different alleles.
(a) Each parent provides a complete set of instructions to each offspring.

11. Passing traits from parents to offspring is called heredity.

12. Mutation
Errors in gene copies can cause somewhat different proteins to be produced

13. Diversity in Offspring
That means a unique egg will be fertilized by a unique sperm to produce a unique child
For each gene, there is a 50% chance of having the same as a sibling

14. Diversity in Offspring
The combination from the parents creates the individual traits of each child
Environment also plays a role, but differing alleles from parents are the primary reason that non-twin siblings are not identical

15. Figure 6.6 Crossing over increases diversity in gametes.
When chromosomes pair at the beginning of meiosis, information may be exchanged via the process of crossing over. (a) In our instruction manual analogy, this means that meiosis can result in the formation of completely new chromosome. (b) A photomicrograph of chromosomes in the process of crossing over during prophase of meiosis I.

16. Twins Fraternal (non-identical) two separate fertilized eggs
not genetically the same

17. Figure 6.7 The formation of twins.
(a) Dizygotic twins form when 2 different eggs combine with 2 different sperm cells, resulting in 2 embryos who are only as similar as siblings.

18. Twins Identical monozygotic: one single fertilized egg that separates
genetically the same

19. Figure 6.7 The formation of twins.
(b) Monozygotic twins form when a newly fertilized embryo splits in half resulting in 2 identical embryos.

20. Gregor Mendel Determined how traits were inherited
Used pea plants and analyzed traits of parents and offspring
Figure E6.1a Gregor Mendel

21. Genotype
Genotype
homozygous: two of the same heterozygous: two different

22. Phenotype Phenotype the physical outcome of the genotype
depends on nature of genes

23. Mendelian Genetics Dominant – can mask a recessive
Recessive – can be masked by a dominant gene

24. Mendelian Genetics Dominant – capital letter For example: T for tall
Recessive – lower case letter
For example: t for short

25. Punnett Squares
Punnett squares are used to predict offspring phenotypes
Uses possible gametes from parents to predict possible offspring

26. Punnett Squares: Single Gene
A parent who is heterozygous for a trait
Aa can produce two possible gametes
A or a
A parent who is homozygous for a trait
AA can only produce gametes with A

27. Punnett Squares
The possible alleles are listed along the top and side of the square
The predicted offspring genotypes are filled in the center boxes of the square

28. Punnett Squares The offspring can be homozygous or heterozygous
It all depends on the parents and the possible gametes
Punnet squares can be used to predict possibilities of inheriting genetic diseases

29. The environment plays a role – traits such as height, weight, musical ability, susceptibility to cancer, and intelligence

30. Environment can affect phenotypes
Identical twins with the same genotypes may not have exactly the same appearance…

31. Figure 6.14 The effect of the environment on phenotype.
These identical twins have exactly the same genotype, but they are quite different in appearance due to environmental factors.

32. Why Traits Are Quantitative
Figure 6.15 Skin color is influenced by genes and environment.
(a) The difference in skin color between these two women is due primarily to variations in several alleles that control skin pigment production.
(b) The difference in color between the sun-protected and sun-exposed portions of the individual in this picture is entirely due to environmental effects.

33. Correlation between Twins
Twin studies allow scientists to test the effects of environment
The DNA is identical in identical twins but the environment may be different
Compare monozygotic (identical) twins to dizygotic (fraternal) twins
Study twins raised together and study identical twins raised apart