1. GENETICS ODDS & ENDS

2. (d) The haplo-diploid system
Different systems of sex determination
are found in other organisms
22 + XX X
76 + ZZ ZW 16
(Haploid)
(Diploid)
(b) The X–0 system
(c) The Z–W system
(d) The haplo-diploid system
Temperature determination- some reptiles

3. Essential knowledge 3.A.4: The inheritance patterns of many traits cannot be explained by simple Mendelian genetics b. Some traits are determined by genes on sex chromosomes.
To foster student understanding of this concept, instructors can choose an illustrative example such as: • Sex-linked genes reside on sex chromosomes (X in humans) • In mammals and flies, the Y chromosome is very small and carries few genes • In mammals and flies, females are XX and males are XY; as such, X-linked recessive traits are always expressed in males.

4. Y chromosome-small & carries only a few genes
Y linked traits show up ONLY in MALES EX: hairy pinna
SRY gene Master control gene turns on other genes Creates a cascade of activation to make developing embryo into a MALE

5. What’s the pattern:
X-LINKED RECESSIVE traits ~ Show up more frequently in males
because they have no back up X
~ Females need two recessive alleles to show the trait.
~ Females can be carriers for X linked traits
~ Male can never be carriers of X linked recessive traits
AUTOSOMAL RECESSIVE traits
~ Both males and females can be carriers for autosomal recessive traits.

6. MALES BB or Bb = bald bb= not bald
Essential knowledge 3.A.4. The inheritance patterns of many traits cannot be explained by simple Mendelian genetics • Some traits are sex limited • Expression depends on the sex of the individual Ex: milk production in female mammals pattern baldness in males.
MALE PATTERN BALDNESS SEX LIMITED (SEX INFLUENCED) AUTOSOMAL- NOT ON A SEX CHROMOSOME BUT SHOWS DIFFERENT PATTERN IN MALES & FEMALES
Almost like B is dominant in males and b is dominant in females
MALES BB or Bb = bald bb= not bald
FEMALES BB = bald Bb or bb= not bald

7. Why don’t genetic disorders “go away”?
SICKLE CELL ANEMIA Mutation in hemoglobin gene Causes red blood cells to change shape in low oxygen conditions More common in African Americans
HETEROZYGOTE ADVANTAGE: 1 sickle cell allele/1 normal allele provides protection against MALARIA
Watch a video about
sickle cell and malaria

8. Connections between
genetic mutations and
resistance to disease.
Sickle cell- malaria Cystic fibrosis- typhoid Tay-Sachs – tuberculosis
AB blood type-cholera Vitamin D receptor-osteoporosis

9. X-chromosome Inactivation
In female cells ONE X chromosome is randomly switched off
It condenses and forms a dense region in the nucleus called a
BARR BODY

10. CAT COLOR In cats the gene that
controls color is carried on the X chromosome Tortoiseshell cats express different alleles in different cells
FEMALE CATS: Female cat can have BOTH
black and orange spots
See a video

11. Dominance & Phenotype- Depends on how you look at it
TAY-SACHS DISEASE
Human genetic disorder in which brain cells are unable
to metabolize certain lipids because a crucial enzyme
does not work properly.
As these lipids build up in brain infant suffers seizures, blindness,
loss of motor & mental function > > > leads to early death.
At ORGANISMAL LEVEL acts as a recessive trait.
Child with two copies of Tay-Sachs allele (tt) has the disorder.
Child with Tt or TT does not (COMPLETELY DOMINANT/RECESSIVE)
At BIOCHEMICAL LEVEL- Tt individual has enzyme activity level in
between the TT and tt person (INCOMPLETE DOMINANCE ?)
At the MOLECULAR LEVEL – Tt individual makes equal number of normal
and dysfunctional enzyme molecules (CODOMINANT ?)
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12. Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2006

13. Karyotype can show: Sex of baby Missing or extra chromosomes
Major deletions or translocations
Can’t see individual gene changes

14. EXTRANUCLEAR GENES
The inheritance of traits controlled by genes present in the chloroplasts or mitochondria
Depends solely on the maternal parent because the zygote’s cytoplasm comes from the egg
EX: Variegated leaves result from mutations in pigment genes located in plastids inherited from mother
Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2005

15. MITOCHONDRIAL DISEASES
Some diseases affecting the muscular and nervous systems are caused by defects in mitochondrial genes that prevent cells from making enough ATP
Accumulation of mitochondrial mutations may play role in aging process, diabetes, heart disease, Alzheimer’s
EX: mitochondrial myopathy-
weakness,
intolerance of exercise
muscle deterioration

16. MONOZYGOTIC = maternal IDENTICAL DNA
DIZYGOTIC = fraternal
DIFFEERENT DNA

17. CONJOINED TWINS
Babies are born
ATTACHED to each other

18. Anencephaly spina bifida
Mages fro:
Some birth defects have environmental causes: NEURAL TUBE DEFECTS (NTD’s)
Anencephaly
spina bifida

19. NEURAL TUBE DEFECTS (NTD’s) Brain or spinal cord doesn’t form properly
Mages fro:
NEURAL TUBE
DEFECTS (NTD’s)
Brain or spinal cord doesn’t form properly
Linked to LOW levels of Vitamin B (Folic acid) in moms’ diet
Important for new cell growth even before mom knows she is pregnant
All women need 400 micrograms (mcg) of folic acid every day
LINK BETWEEN Vitamin B12 and NTD’s

20. FETAL ALCOHOL SYNDROME (FAS)
Images from:
FETAL ALCOHOL SYNDROME (FAS)
Due to mother drinking alcohol during pregnancy
Leading cause of preventable birth defects and developmental disabilities in the United States.
Alcohol passes through placenta to baby
Exposure to alcohol during first trimester can cause major birth defects Later in pregnancy can cause poor growth and brain damage

21. FETAL ALCOHOL SYNDROME (FAS)
Small head/small wide-set eyes
Below average height and weight
Hyperactivity/lack of focus 
Poor coordination
Delayed motor skill development
Learning disabilities
Attention and memory problems
Behavior problems
Poor judgment
Mood swings
100% preventable
Due to mother drinking alcohol during pregnancy
FAS Fact sheet
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