1. Chromosomal Mutations/Abnormalities
Describe processes that can alter composition or number of chromosomes (i.e., crossing-over, nondisjunction, duplication, translocation, deletion, insertion, and inversion).

2. Chromosomal Mutations/Abnormalities
A chromosomal mutation is a change in the structure of a chromosome.
There are processes that can alter the composition or number of chromosomes in a cell(s). These processes include:
Crossing-over
Nondisjunction
Duplications
Translocations
Deletions
Insertions
Inversions
A karyotype, or picture of all of the chromosomes found in a cell, can identify changes to chromosome structure and number.

3. Crossing-Over
Crossing-Over: The exchange (swapping) of segments of homologous chromosomes.
Crossing–over causes gene recombination, or a reassembling of the genes, which increases genetic diversity.

4. Nondisjunction
Nondisjunction – Failure of sister chromatids to separate during mitosis OR failure of homologous chromosomes to separate during meiosis. Nondisjunction results in extra chromosomes in some cells and missing chromosomes in other cells.
Examples of disorders caused by nondisjunction:
Down Syndrome
Triple X Syndrome
Klinefelter’s Syndrome
Turner’s Syndrome
Homologous chromosomes do NOT separate
Sister chromatids do NOT separate

5. Duplication
Duplication: A part of a chromosome (genes) or is copied resulting in EXTRA genetic information.
A duplication results in a chromosome with extra genes. Examine the pictures below:

6. Translocation
Translocation: The exchange of portions of non-homologous chromosomes. (Remember crossing over is the exchange of segments of homologous chromosomes...these processes are their outcomes are very DIFFERENT!)
During a translocation, genes from a pair of autosomes exchanges with a different pair of autosomes. (Genes from one of Pair 13 might swap with genes from one of Pair 2.)

7. Deletion
Deletion: A segment of a chromosome (gene) is removed.

8. Insertion
Insertion: A segment of a chromosome (gene) is added. (SEGMENTS ARE NOT SWAPPED BETWEEN CHROMOSOMES LIKE WE SEE IN A TRANSLOCATION.)

9. Inversion
Inversion: A segment of a chromosome is removed, flipped over, and reinserted back into the chromosome.

10. Identify the chromosomal abnormalities!

11. Introduction to Genetics
BIO.B.1.2 – Explain how genetic information is inherited.

12. A closer look at chromosomes…
Chromosomes are located in the nucleus of all eukaryotic cells.
Chromosomes are made up of long strands of DNA.
A gene is a piece of DNA that directs a cell to make a certain protein. The proteins made are responsible for specific traits. Traits are distinguishing characteristics that are inherited (such as eye color, hair color, etc...).

13. How do we know traits are inherited?
Genetics is the study of inheritance. Inheritance is the process in which genetic material is passed from parents to their offspring.
Gregor Mendel, the Father of Genetics, laid the groundwork for genetics in the mid 1800’s by studying pea plants and their traits. His experimentation on pea plants led to the following conclusions:
1. Traits are inherited as discrete units called genes. Each gene has a locus, or a specific position on a pair of homologous chromosomes.
2. Organisms inherit two copies of each
gene, one from each parent.
3. The two copies segregate during gamete formation because gametes (eggs and sperm) only receive one copy of each gene.
The last two conclusions led to the “Law of Segregation.”
Father of Genetics

14. Alleles
An allele is any alternative form of a gene (variation in nucleotide sequence) occurring at a specific location on a chromosome. Alleles are often represented by letters.
Each parent donates one allele for every gene.
Homozygous describes two alleles that are the same at a specific locus.
Heterozygous describes two alleles that are different at a specific locus. RR Rr

15. Dominant vs. Recessive Alleles
Dominant alleles are represented by uppercase letters; recessive alleles by lowercase letters.
A dominant allele is expressed as a phenotype when at least one allele is dominant. (Rr or RR = dominant; therefore the pea is round). Both heterozygous (Rr) and homozygous (RR) genotypes produce a dominant phenotype.
A recessive allele is expressed as a phenotype only when two copies are present. (rr = recessive; therefore the pea is wrinkled).
Most traits do not follow simple dominant versus recessive patterns of inheritance (ex. Hair color, skin color, eye color, height, etc…).

16. Genes influence the development of traits!
All of an organism’s genetic material is called the genome.
A genotype refers to the makeup of a specific set of genes. Examples: Tt, RR, bb
A phenotype is the physical expression or appearance of a trait. Examples: tall, round, blue
View this video entitled “What are phenotypes?”

17. Punnett Squares
The Punnett square is a grid system for predicting all possible genotypes and phenotypes resulting from a cross.
The axes represent the possible gametes of each parent.
The boxes show the possible genotypes of the offspring.
Punnett squares display
the probability that an
event will occur.

18. Punnet Squares & Probability
Probability is the likelihood that something will occur.
Probability predicts an average number of occurrences, not an exact number of occurrences.
Probability =number of ways a specific event can occur
number of total possible outcomes
Probability applies to random events such as meiosis and fertilization.

19. Monohybrid Crosses
Monohybrid crosses examine the inheritance of only one specific trait. Mendel’s “Law of Segregation” is evident in monohybrid crosses, and states that during gamete formation the two copies of a gene will segregate or separate. In other words a sperm or egg cell does NOT inherit both copies of mom’s genes AND both copies of dad’s genes.
Example: Trait = Fur Color B = brown OR b = white
Bb x Bb B b B b

20. Dihybrid Cross
Dihybrid crosses examine the inheritance of two traits. Mendel’s “Law of Independent Assortment” is evident in dihybrid crosses, and states that allele pairs separate independently of each other during meiosis. In other words the inheritance of one trait has no influence over the inheritance of a different trait.
Example: Trait = Fur color & Fur length

21. Sex-Linked Inheritance
The chromosomes (autosomes vs. sex chromosomes) on which genes are located can affect the expression of traits.
Two copies of each autosomal gene affect phenotype (because autosomes are made of homologous chromosomes); however this is not the case for sex-linked genes because they aren’t always homologous.(genes on sex chromosomes).
Mendel’s rules of inheritance apply to autosomal genetic disorders.
A heterozygote for a recessive disorder is a carrier. A carrier is an individual that carries one gene for a disorder and can pass it on to his or her offspring, A carrier does NOT show signs or symptoms of the disorder.
Disorders caused by dominant
alleles are uncommon.
(dominant)

22. Sex-Linked Inheritance
Males and females can differ in sex-linked traits.
Genes on sex chromosomes are called sex-linked genes.
Y chromosome genes in mammals are responsible for male characteristics.
X chromosome genes in mammals affect many traits since both males AND females have at least one X chromosome.
All of a male’s sex-linked genes are expressed because male’s do NOT have a second copy of sex-linked genes (only one X and one Y).
The gene for color-blindness
is sex-linked and located on
the X chromosome.
B = Normal Vision
b = Colorblind

23. Non-Mendelian Genetics
Many factors can influence the expression of traits. Non- Mendelian Genetics accounts for these factors by studying the following:
Incomplete Dominance
Co-dominance
Multiple Alleles
Polygenic Traits
Epistatic Genes

24. Incomplete Dominance
In incomplete dominance, neither allele is completely dominant nor completely recessive.
Heterozygous phenotype is intermediate between the two homozygous phenotypes.
For example if a red rose is crossed with a white rose the F1 generation would all be pink roses.

25. Co-Dominance Co-dominant alleles will both be completely expressed.
Co-dominant alleles are neither dominant nor recessive.
Example: ABO blood types
“A” blood type is co-dominant to “B” blood type; therefore a third blood type “AB” is formed.
Many genes have more than two alleles and this concept is referred to as multiple alleles.

26. Polygenic Traits Many genes may interact to produce one trait.
Polygenic traits are
produced by two or more
genes.
Order of dominance: brown > green > blue.

27. Epistatic Genes
An epistatic gene can interfere with other genes. The gene for albinism is an example of an epistatic gene.

28. Pedigrees
A pedigree is a chart for tracing genes within a family. Pedigrees allow you to track genotypes and/or phenotypes over multiple generations.